From Attractive Fascinante:

Mizuhara Kana is staying together with his cousin, Shuuya. Kana has a weak heart and Shuuya has been taking care of him. Somehow, Kana felt like a bird locked in a cage and hoped to have some breathing space. A coincidental meeting with the transfer student, Aoi Rin, changed Kana’s life. He fell head over heels into this first love. The mysterious Aoi taught him about the freedom outside the cage, but the risk that came along with this freedom could cost Kana’s life. The love story of a bird flying out of the cage during the summer, will Shuuya rescue Kana in time?