Evergreen (エバーグリーン) is a manga written by Yuyuko Takemiya with art by Akira Caskabe. It began serialization in July 2011 and finished in March 2015. It is complete in four volumes. Seven Seas has licensed it for English release.
Born with a congenital heart disease, and thus unable to join in activities that are too physical, Manga Club Captain Yoshimatsu Hotaka can only watch through the club room’s window whenever the school swim team practices. Hotaka is enamored with swimming ace, Awaya Niki. But sickly, shy and extremely introverted, he feels all he can do is pine for her from afar. Seeing her as a sort of Goddess of Summer, he feels he isn’t even worthy to share the same air with Niki, much less approach her.
But when the gym teacher asks Hotaka to attend a special, after-school swim class to make up for not participating during regular classes-a supposed to be one-on-one student teacher session which the swim team unexpectedly crashes-it sets into motion events that may, quite surprisingly, result into Hotaka and Niki actually becoming friends.
Official English site