NHK ni Youkoso!

Synopsis

Tatsuhiro is desperately attempting to clean his dirty apartment before his mother comes, and Misaki helps him. The two and Tatsuhiro's mother later have lunch in a Chinese restaurant. When Tatsuhiro leaves to go to the bathroom, his mother tells Misaki that she knows this was all a setup because she could always tell whenever he was lying. Tatsuhiro overhears this and starts feeling even guiltier. However, in his presence, his mother goes along with the story and does not give Tatsuhiro a chance to clear himself. Tatsuhiro and Misaki later get carried away with their fake relationship.

(Source: Wikipedia)