Boku no Hatsukoi wo Kimi ni Sasagu

From Tenshi-Tachi:

Takuma and Mayu's story began when they were only 8 years old. During his childhood, Takuma was constantly hospitalised due to his heart condition. He soon became friends with Mayu, the daughter of the doctor in charge of his case. Day by day they grew closer and closer. However, the summer when Takuma was 8, he made a promise to Mayu that he couldn't keep... Their story unfolds as they grow older and their bond gets stronger...

This manga received the 53rd Shogakukan Manga Award for shoujo manga.

Extras:

? V.01 - Motto Ikitai...
There is a ghost looming in a hospital. Two little kids, Mayu and Takumi, are now scared after listening to the ghost story from a nurse. Was the story told by the nurse true or not? The kids decide to find out.

? V.07 - The Things I Want

? V.11 - Kare wa Ike mo Shinai Sarukoen wo Mezasu