Warui Otona ni Narimashite
悪い大人になりまして
Natsuno, without a home after a breakup, stays in his office. At a wedding, he runs into Ui, a former classmate who had confessed to him before graduation and was turned down. Ui now has amnesia and doesn't recognize Natsuno. To get a place to stay, Natsuno tells Ui, "I'm your ex."