Saku Hagita

Hagita is a regular student in Nagano who becomes very good friends with Kakeru. While he is not outgoing or charismatic, Hagita has a profound determination and intelligence. Hagita is a very big fan of reading manga and watching the television show 'Yuugata Get'. Later in the story, Hagita even goes as far as to buy Kakeru manga for his birthday. Throughout the story, subtle comments and interactions hint at an affection Hagita holds for Murasaka and in the future time line Hagita is married to Murasaka.
At the end of the third volume, it is revealed that Chino, Murasaka and Hagita received a letter from the future.

Hagita is the reason Kakeru did not use his bicycle in his suicide attempt like the letters said he would. Before Kakeru left his house on February 15th, Hagita tampered with Kakeru's bicycle so it would be unusable.