Sutekina Doutei Samurai.

Tatsuya, an unemployed virgin, is hired at a Japanese sweets shop run by his classmate Maki, but is shocked to learn that Maki, whom he has a crush on, is engaged. At that time, Tatsuya's older brother leaves behind a Japanese sword that was a keepsake from their father. Tatsuya accidentally peels off the amulet that was attached to the sword...