犬も歩けば恋がはじまる@発情期

Hometani Sora, a plain high school student, unexpectedly begins dating his crush, Matsuda Makito, thanks to his unique ability to transform into a Pomeranian at a moment's notice. As they navigate their newfound relationship, the first mating season arrives. When Sora falls ill and misses school, Makito grows worried and decides to visit him at home... (Source: Ichijinsha, translated)