YOZORA NO SUMIKKO DE,

Hoshino is a timid grade school teacher. Sudou was one year his senior in high school. They meet again for the first time in over a decade and discover that Sudou's son is Hoshino's student. The two of them try to figure out how they feel about each other, and try to remember what it was that had brought them together and ultimately drove them apart in high school. They're both different, but that may not matter as much as how they still feel about each other. — Description from AniList community (anilist.co).