Koi ni mo Naranai.

From Hoshikuzuu Scans:"That's the first time I've seen crying so beautiful." Tajima finds himself taken in by Koga's crying face, but little did he know, the reason behind those tears was the death of his goldfish at the hand of Tajima's cat (Buuta). While figuring out how to apologize for that, he stumbles across a secret of Koga's.