Once you're at the very final point of the game, you're in a throne room and tasked with making dialogue choices, which result in different endings. None of these endings are missable as you can reload your clear game save data over and over and keep redoing the fight. This one is as follows;
Once you're in the Throne Room, you're met with a choice, and many more choices depending on which you pick.
1) Defend the cycle of reincarnation.
2) Reject the realm and slay the Oni.
Choosing option 2) will task you with two boss fights, which will lead you onto the next series of choices.
After the final oni boss fight, you're given a choice to Kill yourself, or Live.
If you choose to Live, you'll be given this trophy after some cutscenes and the credits.