Suki ja nai kedo Aishiteru

Kouki Hanashima and Asahi Hidaka are in a class-recognized relationship that experiences fluctuations in their dynamic. One day, Kouki's older sister unexpectedly places her infant son with the couple, explaining that her job as a stewardess will keep her away for a month. The child is also named Asahi, and he appears to be competing with the older Asahi for Kouki's attention.