Otoko no Isshou

Douzono Tsugumi, who works in a major electronics company in Tokyo, is spending a long holiday at her grandmother's house at the countryside. Her grandmother passes away, and Tsugumi decides to live in her house and work from there. The next morning, an unknown man in his 50s arrives to the house. Appears that the man is Tsugumi's grandmother's student and has been given a key to the house. Tsugumi doesn't quite understand the relationship her grandmother and the man had, but he moves in to be Tsugumi's roommate.
(Source: Stiletto Heels)