Conceptual_Entity
why not make him have a curse energy sealing technique? no matter how strong a person is they can even be killed or sealed like Gojo who was sealed by Kenjaku and to open it takes a lot of effort from outsiders.... just give mc a technique that can seal other people's cursed energy which will be a trump card when fighting the enemy, if you don't want it to be too strong just give some terms or conditions to seal that person's cursed energy