Carbonic Acid - Act Up

As Winter settles in, Tooru finds an abandoned kitten and decides to take care of it. After showing the cat to the others, Tooru goes with Run to visit a pet shop and a family restaurant, where Run comes with a name for the cat, Tansan. The next day, snow falls at school and the students have fun playing in the snow, except for Nagi who is noticeably bothered by the cold. By the next day, however, everyone but Nagi catches colds.