Grants access to the subquest "The Doctor's Last Wish". In this quest, players will be able to take on "Tyrant Mephisto," and even recruit him should they prove victorious.

*After progressing to a certain point in the game, talk to the Bethel researcher in the Tokyo Diet Building to begin the subquest. Once completed, you will have the option of fighting Mephisto as many times as you want.
*It is recommended that this subquest be attempted near the end of the game.