Tsumasaki ni Kourozu

One day, Iwai, an ordinary college student, is suddenly offered a part-time job to work as an assistant for the mycologist, Murota, a seemingly moody and unsociable man. Though things start off a bit rocky, Iwai soon finds that he not only enjoys spending time with Murota and learning about a world previously unknown to him, but he also likes taking care of the man when he neglects to take care of himself. However, joy is gradually replaced by unrest, as Iwai becomes increasingly aware that his feelings towards the man may be deeper than he originally thought. (Source: June Manga)