Kimi no Suizou o Tabetai

Shiga Haruki happens to find a diary in a hospital one day. The diary belongs to his classmate, a girl named Yamauchi Sakura, who is revealed to be suffering from a terminal illness in her pancreas, and who only has a few months left to live. Sakura explains that he is the only person apart from her family that knows about her condition. He promises to keep it secret and, despite their completely opposite personalities, decides to be together with her during her last few months.Source: ANN