When Mitsuha Kawase reunites with some of his old friends, he is surprised that one of them is employing Nana, an amnesiac who has the same name as his long-lost brother. As Mitsuha and Nana share a room and bond over the next few days, Mitsuha cannot help but notice some odd similarities between Nana's past and his brother's.

Elsewhere, Hiromu has had persistent concerns that he is actually adopted since he bears little resemblance to his parents, but he has always been comforted by his older brother, Nanao. As they have aged, however, their relationship has become more complex, and Hiromu realizes he harbors feelings he cannot speak aloud.