Sora no Iro, Mizu no Iro

Asa & Natsume are both in love with Hajime Saisho. Instead of fighting over him, they both promised to share him equally. However, both girls have to leave him by the end of the summer. As the summer days go by, they each spend their precious time with Hajime, while the day of their fated departure draws near.

(Source: Anime News Network)