Nasu to Altair

Manda Mitsuo is a 16-year-old high school student who lives with his stepmother, after his father's death. Manda Minato, his stepmother, is only 31-year-old, and was his father's former student. She also happens to be adorable, which constantly triggers Mitsuo's painful reaction to extremely cute things. At school, a very intimidating girl, Kitou-san, is also trying awkwardly to get closer to him. They and other friends at school make up the fabric of Mitsuo's unusual daily life.

(Source: MangaHelpers)