Hosaka was born in Yamanashi prefecture and received his undergraduate education at Waseda University with a major in political science and economics. After graduating he worked for Seibu Culture Centers, holding popular educational workshops on philosophy. During this period (1990) he published his first book, Plainsong. He left Seibu in 1993 to devote his efforts to writing full time, with the assistance of fellow writer Nobuo Kojima.
Hosaka writes about ordinary people in ordinary life situations. His work has been compared with the movies of noted director Yasujirō Ozu. A common theme in his writing is the presence of a cat in the lives of his characters.