The Star Who Loves the Moon starmoon

Lucine wants to die when she turns 18. She often writes her unconventional thoughts about life and death in papers that she slips into library books. One day, Orion discovers her little hobby and is awed by her talents for words.

Unlike Lucine, Orion is a cheerful guy with lots of friends and lots to live.
Unlike Lucine, Orion loves to love and isn't afraid to get hurt.
Unlike Lucine, Orion hides many secrets.

When Lucine tells Orion her plans to die when she turns 18, Orion doesn't object, doesn't ask her to reconsider; he doesn't even blink. He only asks one thing:

"Then live the rest of your life with me, and write lyrics for my band."

Despite herself, Lucine agrees to his plea.