The Devil Is Troubled By The Suicidal Heroine

This is a manga where an bikini clad overpowered heroine named Mana hates being immortal and wants to somehow kill herself, so she goes to the Devil King to find a way to kill her. The formula usually goes, the Devil King comes up with a new plan, usually involving some weird magic to try to finish off the heroine but fails(usually because she's too overpowered) and prepares a new one next time, rinse and repeat.

Chapter 6: The Heroine Is Corrupted
This chapter, the Devil King plans instead of killing her, he could instead brainwash Mana into becoming his completely obedient servant. First, he tried making her loyal but that didn't go very well because her loyalty causes her to still want to stop herself from killing her master once the brainwashing wears off, still yet by killing herself. Then the Devil King decided to do over by brainwashing Mana into loving him which causes the heroine to try to do the very thing she wants to do with the one she loves, double suicide. But then the spell on Mana breaks, waking her up, the Devil King then asked her if she still loved him, being out of the loop, Mana asked the Devil King where he got that confidence from.