Cotton

From Kotonoha:

One rainy day, the young woman Natsuki encounters a high school student in the street. Acting on an impulse, she gives the girl her umbrella and walks away. It turns out later that the girl, Michiko, is the younger sister of Natsuki’s sister’s newly-married husband. Even though Michiko has a difficult personality and doesn’t open herself to others easily, she seems to be attracted to Natsuki. Thus begins an unusual friendship between two unlikely characters who need each other more than they first realize…

The main story (Cotton) was released as four chapters. There are also four additional stories:

Story 2: Creature
Story 3: Asa no Kodomo
Story 4: Tegami (Letter)
Story 5: Zange