Boku to Jinginaki Ojisan

The story follows Yuuhi, an elementary school student who is home-sitting alone every day. One day, all of a sudden, his neighbor, Mr. Aoi, who lives upstairs, falls in his room leaving a hole in the ceiling. Yuuhi finds out that his neighbor is a cool looking man with a secret side he doesn't want anyone to know. What does he want to hide so badly? The comedy about a good-looking gangster and a kind-hearted boy and their secret is ready to start!

(Source: MANGA Plus)