Alliance of the 15s

Alliance of the 15s summary:

Ryoichi, a soft-spoken and quiet fifteen year old, meets Naomi, a young girl who is battling a life-threatening illness through her childhood friend, Tetsuya, who is the ace player of their school’s baseball team.
As they become closer, she opens up to him about her fears and secrets, and he also comes to deeply care for her. But one day when he visits her at the hospital, she suddenly asks him: “Why don’t we commit a double suicide?”