Grants access to the subquest "A Goddess in Training." In this quest, players will be able to take on "Megami Artemis," and even recruit her 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 Artemis as many times as you want.
*It is recommended that this subquest be attempted at least halfway through the game.

More details on the official game page of A Goddess in Training ...