On the day before winter break, following a brief period of peace after the desire unleashing incident, a new phenomenon takes place in which Iori and Yui temporarily revert to children from noon to five o'clock in the afternoon that day. After returning to normal, they lose memory of what happened, but remember things from when they were that age. Later that night, a second Heartseed appears before Taichi through his younger sister, Rina Yaegashi, tasking him to watch over the others and warning him not to tell the others about his existence. The next day, Taichi stumbles upon Yui, who is argued at by an old karate rival, Chinatsu Mihashi, over breaking a certain promise which she cannot remember. As the gang meets up at an abandoned building, this time Himeko and Yoshifumi shrink, with the now ten-year-old Yoshifumi likening Yui to a girl named Nana Nishino. After reverting to his normal age, Yoshifumi explains that Nana was a girl he went out with once before she moved, leading him to be conflicted over how his feelings stand for both her and Yui. The next day, as Taichi and Himeko watch over a fourteen-year-old Iori, Himeko voices her worries.