とある街にある昔ながらの佇まい『アパートの清水』――。
そこでは今日も、売れない漫画家・狩野進（横山裕）が締め切りを迎えて早々に彼女にフラれるところを同じ階の秋友美月（山本舞香）に冷めた目で目撃され、その騒がしさの中でも、訳あって１人暮らし中の少年・さとうコタロー（川原瑛都）は静かに朝の準備を進めていた。
この春からめでたく小学校に入学したコタロー。ランドセルを背負い、１人で小学校に通っていく姿を、狩野や美月、そして１階の田丸勇（生瀬勝久）は頼もしくも少し寂しい気持ちで見送るのだった。
"Shimizu Apartment" has an old-fashioned atmosphere in a certain town.
There, as usual today, struggling manga artist Kano Susumu (Yokoyama Yu) is dumped by his girlfriend early as his deadline approaches, and is witnessed with a cold look by Akitomo Mizuki (Yamamoto Maika) who lives on the same floor. Amid the commotion, Sato Kotaro (Kawahara Eito), a boy who lives alone for some reason, is quietly getting ready for the morning.
This spring, Kotaro has happily started elementary school. As he shoulders his school bag and heads off to school alone, Kano, Mizuki, and Tamaru Isamu (Namase Katsuhisa), who lives on the first floor, see him off with a feeling of reassurance but also a little loneliness.
