Ekubo!

Shibutani Junpei has a crush on a classmate, Mizusawa Nana. He works part time at a fast food restaurant, and his boss has seen a love letter he wrote. His boss wants to hire at least one female employee, but he has a tendency to drive them off, so he steals the love letter and posts it on a bulletin board, altered somewhat a to the shock of both men, it works, and Nana answers the letter and comes to work in the restaurant.

(Source: Animeraider)