The Legend of the Strongest, Kurosawa!(2003)

Saikyou Densetsu Kurosawa

Kurosawa is sick and tired of his boring, ordinary life growing old as the less popular site foreman in Anahira Construction. The turning point comes when his 44th birthday comes along, and no one remembers or celebrates with him. Realizing he lived a life without drive or purpose, Kurosawa tries to go past his comfort zone to turn his life around. Will his newfound shenanigans help him or hurt him when he gets caught up in fights with delinquents?

(Source: Manga Planet)