This is Saskue you and him are going on a mission, Naruto and you go on a mission together it’s said to be a D-rank mission, which means it’s not that hard. But when you defect one of the enemy’s the other one runs away Naruto/you runs after him so Saskue follows. They both fall into a box that’s quite small and find that this isn’t a D-rank mission at all, the box is unbreakable, but the demon simply wants your chakra. The demon itself doesn’t have a heart so the only way to escape from certain death is through love.