Tsukasa Domyoji moves in next door to Tsukushi Makino, but finds that he cannot sleep at night. Tsukushi starts to feel a little sad with him not being around. One night, she discovers him going into his apartment and confronts him.
Tsukushi Makino wakes up feeling grumpy, having hardly sleep all night. After making breakfast, her brother Susumu suggests taking over a plate to Tsukasa Domyoji. However, when she opens his door, Tsukasa is not there. At school, Tsukasa confesses to Akira Mimasaka and Sojiro Nishikado that he cannot sleep there. Tsukushi listens in on their conversation. Tsukasa then leaves to go sleep. Akira asks Sojiro about Yuki Matsuoka. Sojiro admits that he brought her to a hotel, but nothing happened.
Tsukushi catches up with Sojiro, planning to confront him about Yuki. He manages to "skirt the issue" by talking about Tsukasa living next door. She brings up Yuki, asking him to "stop seeing her if [he is] just stringing her along." Instead of answering, Sojiro brings up a hypothetical situation asking "What if Kazuya likes you?" She eventually answers that he is only a friend and that she "[does not] see him as a male." Sojiro snaps his fingers and says "And that's exactly how Yuki is to me," before walking away.
That night, Susumu mentions that Tsukasa has not come by lately. He wonders if Tsukushi is "just a novelty to him." Tsukushi declares "He's not like that!," though she secretly feels insecure. Tsukushi falls asleep thinking of Tsukasa. She wakes up in the middle of the night after hearing some noises. Tsukushi discovers Tsukasa sneaking into his apartment. Noticing her annoyed expression, Tsukasa states that he "come and go as [he pleases]." Tsukushi then suddenly "But this is my world!" and starts crying.