Would You Like to Be a Family? Part 1

Volume includes: 
1-2. Kazoku ni Nattemimasen ka? (家族になってみませんか?, Would You Like to Be a Family?) 
Takemura is a distant, workaholic designer in the planning division. While most of his officemates had given up on interacting with him, his loud co-worker Masaki Natsui is persistent on breaking his indifferent demeanor. When one trip to the convenient store leads to Takemura crossing paths with Masaki and his adopted son, Mori, everything changes for Takemura as he is pulled into a somewhat makeshift family dynamic with the two. 
 
3-4. Kuma no Kimochi (くまのきもち, Kuma's Feelings) 
5. Hajimete no Renai Shinrigaku (はじめての恋愛心理学, The First Love Psychology) 
 
(Source: Futekiya) 
 
Note: Chapter count includes one extra related to the first story.