Inu mo Arukeba Koi ga Hajimaru@Inumimi

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. The two promised to go on a trip during Golden Week. However, the night before their departure, Makito wakes up to find that he has sprouted golden ears!

(Source: Ichijinsha, translated)

Side story of Inu mo Arukeba Koi ga Hajimaru.