This summer vacation begins with a car accident...

Our protagonist protects a man from an out of control car, but gets hit and loses his memory in the process. The man he saved happens to be the owner of a jazz bar, sótano. Out of sympathy for his hapless savior, the man decides to set him up with a job and a place to live.

From the outside, sótano looks like a cozy little jazz bar, but behind the scenes they solve problems that the police and legitimate detective agencies won’t touch. The staff there give our protagonist the name "Haru". He gradually makes his way deeper into the organization, and the hearts and lives of the staff, while working as an apprentice bartender. But just who is Haru really...?

[From Mangagamer]