Kaiji Hozumi is a minor supporting character from the anime and light novel series The Testament of Sister New Devil (Shinmai Maō no Testament). He is a massive fan of Yuki Nonaka, openly demonstrating his heavy admiration by referring to her affectionately as "Princess Yuki". Because of his intense crush, he is highly prone to jealousy. He feels heavily bothered and bitter when the newly transferred protagonist, Basara Toujou, acts close and friendly with Yuki. He wishes he could occupy that same close space in her life, making him resentful of Basara's easy integration into her circle.

Chaos in The Testament of Sister New Devil (Shinmai Maō no Testament) refers to a major antagonist character in the story. Chaos does not have complex moral grey areas—he is a manifestation of raw, chaotic destruction. He views everything around him—whether it's humans, heroes, or the demons who were foolish enough to unleash him—as mere obstacles to be stepped on. He possesses an utter indifference to life; he doesn't hate his enemies so much as he simply finds their existence irrelevant.

Madonis is a villainous supporting character in the light novel, manga, and anime series The Testament of Sister New Devil (Shinmai Maō no Testament). Madonis is a textbook antagonist who views others strictly as tools or obstacles. He shows a complete lack of empathy for both his subordinates and the general population of the Demon Realm. True to his sin of "Greed," his actions are driven entirely by a thirst for absolute control. He believes himself superior to the younger generation of demons and handles his political influence with immense cruelty. He is entirely willing to execute mass massacres and genocidal plots within the Demon Realm to consolidate the Council's power and eliminate political opposition. Madonis serves as one of the behind-the-scenes instigators plotting against the main cast. However, his arrogance ultimately leads to his downfall. He meets a swift and grim end when he is decapitated by Liala, the younger sister of the previous Demon Lord, serving as a brutal poetic justice for his manipulative schemes.

Admirath is a wind demon. He appears in Episode 8 of Season 2 (Burst) for a match against Kurumi Nonaka and shows her one of Basara's coat button, telling her that Basara's fate lies in her hands to reduce her confidence and prevent her from going all out. During their match, it was commented by Leohart & co. that though they were fighting fiercly, were not fighting with full strength. He still defeated Kurumi. When Admirath was about to kill off Kurumi, Zest interfered to protect Kurumi. Admirath is a cool, calm and collective demon, willing to show kindness when needed. But in reality, he is a deceitful and sadistic person that cons people into underestimating them. When in battle, Admirath becomes brutal and shows no mercy to his opponents.

In The Testament of Sister New Devil (specifically during the BURST season), Gald serves as a top general and key military asset under the Demon Lord Leohart's faction. Gald strictly views war and combat as a profession. He behaves like an upfront, traditional military man—he doesn't harbor petty malice or personal hatred toward his opponents. Before attempting to execute Basara, he politely tells him, "Nothing personal," proving he views bloodshed strictly as duty. Gald possesses an obsessive, blinding sense of devotion to his orders. He has a bad habit of overworking himself to a dangerous degree. In the light novels, he becomes so entirely consumed with desigiling an ancient relic that Lord Leohart himself has to explicitly command him to take a rest so he doesn't drop dead from exhaustion. Despite his honorable warrior code, Gald is prone to overestimating his situational dominance. During his intense clash over the city of Wilbert, his tendency to drop his guard and engage in "evil gloating" directly gives Basara the opening needed to cut his arm off using the Banishing Shift technique. He possesses incredible survival instincts. Even after being targeted and severely blasted by the treacherous Nebra, Gald manages to survive the ordeal (a "Disney Death"), eventually being rescued by Lars and returning to Leohart’s side.

Shouhei Donoue is a minor character from the anime and light novel series The Testament of Sister New Devil (Shinmai Maō no Testament), appearing specifically in the sequel series The Testament of Sister New Devil BURST. Shouhei Donoue is characterized primarily as a hot-headed high school delinquent. He is quick to anger and easily provoked, often reacting with his emotions rather than logic. He acts as a typical high school punk, hanging around in a gang at Hijirigasaka Academy. He and his group pick fights out of petty jealousy—most notably confronting the main protagonist, Basara Toujou, after becoming envious of Basara's proximity to popular girls like Mio and Yuki.

Claus is a prominent demon character and leader belonging to the Moderate Demon Faction in the anime and light novel series The Testament of Sister New Devil BURST. Portrayed as an honorable warrior, a competent ruler, and an anti-villain who remains polite even toward his enemies

Ramusas is the older brother of both Wilbert and Sapphire as well as being the acting leader for the Moderate Faction, which his little brother, the previous Demon Lord formed before his death. It also makes him the uncle of Basara Toujou, Mio, and Maria Naruse. But later, it was revealed that he is Wilbert in an alias and Mio's father. Not much is known about Ramusas' personality, but he seems to take his duties very seriously.

Jin Toujou is the father of Basara Toujou and is a living legend among the Hero Clan renowned as the War God. He is also the lover of both Sapphire, the younger sister of Wilbert, and one of the Ten Gods, Raphaeline. After Jin fulfills the wishes of his wives to stop the conflict between Demons and Heroes and deal with his personal business, he travels to a Divine Realm to free them and is currently engaged with the Ten Gods. Jin seems to be usually relaxed and carefree, but he can be very serious as seen when he explained to Basara Mio Naruse's situation. According to Basara, Jin hated the Village of Heroes and its Elders ever since their decision to seal Basara, after the incident with his Banishing Shift, then later decided to banish him instead after complaints from him and others who were on his son's side. However, it seems that he still holds significant sway over their decision making, as he managed to convince the Elders to change Mio back into a "target of observation" and to have Yuki live inside the Toujou Household, instead of confining her to the village as punishment. He, like Shiba Kyouichi, is also aware of the true nature of the Hero clan, as well that most of the highter-up tier is corrupted including the leader of Hero Clan, Albareos. Jin loves and cares deeply about his son as he abandoned his duties as a Hero, so that he could raise him without intervention from the Hero Clan and also being a living remembrance of his lovers. He was also considerate to the dangerous situation that both Mio and Maria Naruse were in as he realized their initial intention in taking over their house as their base, even letting them continue to live with Basara believing the latter could handle taking care of them in his absence. Thus much like his son, Jin values family above anything else, for him it is far more valuable than the Village or the Hero Clan as such.

Wilbert is the previous Demon Lord who was hailed as being the Strongest Demon Lord and Founder of the Moderate Faction. He is also the older brother of Sapphire, the husband of Ashe, and the father of both Mio and Maria Naruse. Prior to his death, Wilbert transferred his demonic power to his oldest daughter, then sent her to live a peaceful life in the Human World with his two trusted demons. In Volume VIII, it was revealed that he faked his death to rebuild the politics of the Demon Realm under the alias of Ramusas, his older brother whose existence he created. Although Wilbert hasn't been seen in his appearance, he has been stated as being a clever and peaceful man who, unlike most previous Demon Lords and Warhawks, doesn't seek war against the heroes and gods, seeking peace between their races. Wilbert also cares deeply about his older daughter choosing to transfer his demonic power into her to ensure that she would remain safe in the Human World under the guard of two trusting demons who acted as her adoptive parents. Wilbert is also extremely dutiful in his mission to ensure peace in the Demon Realm as he not only sacrifices his immense power, but also fakes his own death in order to rebuild the political system inside the Demon Realm due to the Warhawks and Seven Cardinal Sins from behind the scenes. Wilbert is also trusting as he continues to talk with Jin Toujou, one of their more dangerous enemies and biggest threat in the Great War to establish peace between both the demons and heroes. As Ramusas, he believed that Basara was able to protect both of his daughters, but despite his kindness, he was in fact angered after hearing that they had lost their purities and were pregnant.

Volga is a minor demon antagonist from the light novel, manga, and anime series The Testament of Sister New Devil (Shinmai Maō no Testament). In The Testament of Sister New Devil, Volga shares an identical personality with his older brother, Valga. Volga possesses extreme confidence in his demonic powers. He openly mocks his opponents and looks down on humans and the Hero clan, completely underestimating their tactical capabilities. Much like his brother, he firmly believes that raw power and physical supremacy solve everything. He lacks strategic depth, relying entirely on his reinforced muscular body and brute strength to overwhelm enemies rather than using complex magic or intellect. His arrogance ultimately leads to his immediate downfall. During his fight against Yuki Nonaka in the tournament arc, his inability to comprehend that an opponent could match or surpass his physical durability leaves him wide open, resulting in his instant defeat.

Valga is a muscular, tall, and aggressive demon belonging to the current Demon Lord faction in the light novel and anime series The Testament of Sister New Devil. Valga possesses a highly aggressive, combative, and power-hungry personality. As a demon serving the current Demon Lord faction, his worldview is entirely dictated by raw strength. Valga firmly believes that power is the answer to everything. He holds no interest in diplomacy or peaceful resolutions, relying solely on his physical dominance to overpower obstacles. He is a battle-hungry fighter who actively enjoys attacking his targets and thrives in the chaos of a confrontation. Operating as an assassin, he demonstrates zero mercy toward his targets (Mio Naruse and her companions), utilizing his massive frame and immense physical power to deliberately inflict maximum pressure during an assault.

Shuuya Nonaka is the husband of Kaoru Nonaka, as well as the father of Yuki and Kurumi Nonaka. He appears in volume 9, as he was sent to pick up his daughters, Basara, and the others after being summoned by the Elders. He is also been a close friend to Jin Toujou since the Great War. Shuuya is also a strong candidate for being one of the next Elders and later becomes an Elder at the end of volume 11. Shuuya is shown to be a very courteous person as he went to pick up his daughters along with Basara and Mio after being called by the Elders. In spite of being a hero and Mio being considered a potential threat by the current Elders, he was very kind and understanding of the latter, and he even apologized beforehand if anything were to happen. Shuuya is also loving towards his daughters, not blaming them for being involved with helping the daughter of the Demon Lord, as well as him being understanding toward their decision to leave the clan instead of getting him and their mother involved in whatever trouble that they cause in the future. Unlike most of the villagers, he still maintains the exact same level of trust and faith in Basara, even leaving his daughters under his care.

A teacher at Hijirigasaka Academy. Initially assumed to be a human, it is revealed that Mamoru Sakazaki is actually a god like being called Ornis. He is intent on killing Basara, who he believes reached beyond his stature through earning Hasegawa's affection, and believes that killing him will bring Hasegawa back to heaven. After using Kurumi as a hostage to prevent Basara from attacking, he then succeeds in cutting off Basara's sword arm. However, this causes the sword to react and release the spirit of Brynhildr, one of the most powerful Valkyries. In this form Basara's arm grows back, his hair changes color and his right eye glows. He moves so fast that Sakasaki cannot even see him, and he cuts off the top of his foot using Banishing Shift, which he could earlier only use as a counter, not as an attack. Basara attempts to kill Sakasaki but Hasegawa intervenes. She then reveals that she always knew that Ornis has replaced the real Sakasaki. Using her full power, Hasegawa kills Ornis and has Basara take the credit for killing the god.

Shiba Kyouichi is a powerful Hero that the Vatican made using DNA from Jin and a High-Ranking Demon, but was later imprisoned inside the Japanese Branch of the Hero Clan. In Volume II, he was partnered with Takashi Hayase, Kurumi, and Yuki Nonaka as an Observer to eliminate Mio Naruse who had been deemed an S-Rank Elimination Threat, but the missions later ended after she was changed back into an Observation Target. He later became the main antagonist in Volume IX, X, and XI in his attempt at revenge against the entire Hero Clan. After his defeat in Volume XI, Shiba became the sixth servant of Basara by using the Master-Servant Contract with his power. He now works for him as both a personal detective and right-hand man as his trump card for an eventual fight with the Ten Gods. Shiba has displayed a calm and joking personality to the point of seeming almost nonchalant about everything, it is also noted that he showed no contempt toward Basara for losing control over his Banishing Shift five years ago, unlike Takashi and Kurumi whom he had to rein in. It is also shown as he shows neither anger nor surprise toward Takashi despite him using Byakko to shut him outside of the barrier used to fight against Basara. Despite his nonchalant demeanor, Shiba does take his responsibilities as a hero seriously, and he is noted to be quite intelligent and level-headed. He thought seriously about several locations where the seven of them could step up a proper barrier for their fight that wouldn't cause trouble with the spirits and/or the innocent people if it broke. He is also shown to be loyal to the Hero Clan and Elders despite being imprisoned for causing a certain "incident" as he followed their orders to the letter without question as he was sent to eliminate Mio as an S-Rank Target. Shiba also initially stopped Kurumi and Takashi from fighting in the barrier that the deceased Valga stepped up.

Takashi Hayase is a member of the Hero Clan in Japan and childhood friend of Basara, as well as Yuki, Kurumi, and Celis. He was soon partnered with Shiba, Kurumi, and Yuki as ordered by the Elders who changed Mio Naruse into an S-Class Elimination Target instead of just an Observation Target, but later lost against Basara after Byakko went out of control and Mio was changed back to an Observation Target. Being a member of the Hero Clan, Takashi upholds the principle to defeat demons no matter the cost, even if that demon hasn't done anything wrong first as shown when the Elders changed Mio into an elimination target. He has also shown to be quiet hostile toward his former friend, Basara who was assisting Mio despite being a former Hero and even claimed to have become far stronger than him who was viewed as a genius, though this is likely due to the strain in their relationship from childhood due to Basara's forced departure by the Elders. After Yuki started to protect Mio from him and even attacked Takashi, he didn't hesitate to attack back and even kill her if necessary. In battle, Takashi is shown to be calm and collected in dangerous situations as he fought back both Mio and Maria in combat using the best of his abilities to overpower them in combat. After their battle ended in Volume II, Takashi started to settle down, as whenever it comes to Basara, Takashi is a bit of a tsundere and still considers Basara to be an important childhood friend. After six months, he has softened to his original view on Basara and the others, even using the power of Sheila along with Celis in facing Shiba, despite knowing that it could be viewed as a betrayal by the Elders.

Balflear was one of the loyalist supporters of the current Demon Lord, Leohart who acts as both courtier and trusted agent when spying on the Demon Council. After the events of Volume XII, he disappeared during the decisive battle with the Demon Council, then returned under the alias "Cleo Angeles" and was later revealed to be the partner of Shiba Kyouichi. Balflear at first appears to be highly loyal and respectful to Leohart as noted, referring to him in a respectful manner when interacting with him. He always went to spy on several of the Demon Council for his best interests for the Demon Realm. It is noted that Balflear maintains a calm and serious demeanor no matter the situation. Balflear is an opportunist, and he is willing to play whichever side best suits his agenda. He's also driven by his desire for revenge against those who wronged him in the past.

Zolgear was a demon who lived in the Demon Realm and one of the antagonists of the series. He is the father and creator of Zest, his former servant who had worked for him until he abandoned her due to her inner desires and jealousy toward Mio and Yuki. Zolgear is later revealed to be a member of the Cardinal Sins among the Demon Lord Faction in Volume V, him being Lust and the lowest-ranked member. Like most in the Demon Council, Zolgear is ambitious and ruthless even desiring to overthrow the Demon Lord, Leohart replacing him as the ruler of the Demon Realm. He also has no issues with killing people as he murdered both the foster parents of Mio Naruse who had been in charge of her right in front of her eyes, as well as being willing to use anything and anyone to get his way like using Maria's mother as a hostage to force her to bring Mio to him to save her. Befitting his ranking as Lust, Zolgear has a desire for both power and women, as he desired both Mio, as well as the power that she had inherited from her father. He also desired to even take Yuki for himself after her attempt to rescue Mio. Zolgear is also a sadist as he desires to force several female demons into master-servant pacts using the curse of the succubus to hurt them.

Leohart is the current Demon Lord who lives in the Demon World, and he is also the younger adoptive brother of Liala. Leohart is a highly intelligent and powerful yet a relatively young demon. Although he maintains a calm and collected demeanor from a young age, he has been driven by a hatred of the Demon Council and love for his adoptive sister and the demon world as a whole. Leohart despises the constant warring between the various demon factions and dreams of one day creating a united and peaceful world for he and his loved ones to live in, and towards that end, he greatly desires to kill the members of the Demon Council, which he perceives to be at the heart of the corruption in the demon world. Unlike most of the demons who are mostly cruel, selfish, and power-hungry using their subordinates as mere tools, Leohart deeply cares about them as he prevents them from interfering in his clash with Jin, knowing they are no match for him. He also sends Lars to rescue Gardo after he was impressed. Leohart is also trying to prevent unnecessary loss of life as this is seen when he proposed a decisive battle with only a few elites from each Faction to avoid them.

Yahiro Takigawa as he first introduced in his human form to Basara and the others, but his real name is Lars. He is a demon who worked for the Moderate Faction as a double agent among the Demon Lord Faction and was sent as the observer for Mio Naruse under the guise of a student in Hijirigasaka Academy. Throughout the series, Lars has shown different personality traits in both his human and demon aliases. In his initial encounter with Basara, he has proven to be friendly and outgoing, being quick to befriend him after being immediately hated by the male students on his first day due to his connection with Mio and Yuki. Despite that he decides to befriend Basara, Lars never hesitates to leave him behind when Basrara gets caught up by the fans of Mio and Yuki. Under his true identity as Lars, he has shown to be ruthless and cold-hearted as he attacked Basara, Mio, and Yuki on multiple occasions as the "Masked Demon", even having one of the demons under his control stab Basara in the back. However, his cold-hearted side was due to him maintaining his cover as an undercover agent inside of the Demon Lord Faction, which was noted as he had one of the Shadows hit Basara in a non-fatal spot. Throughout his conversations with Basara, he is noted to be fairly lazy and complains about his ever-growing workload over the course of the series. When it comes to school work, Lars often just uses magic in order to finish his assignments or pass exams since it doesn't really impact him. Even in life-or-death battles, he's often seen complaining about the opponents he's tasked with fighting against. Similar to Basara, Lars can be even more ruthless if someone that's targeted is someone important to him as noted when he developed deep-seated anger towards Zolgear who murdered Mio's foster parents (the two people he looked up to as an older brother and sister figure) who took care of him and other orphaned children like him.