Quickly Rewind to the Years When I Wasn't a Dog Licker

Woo Woo Woo Looking for a Book. Quickly Travel to a Certain Plane in Bg. the Heroine Returns to the Small World to Look for Fragments.

The female protagonist enters the stage for the first time and falls in love with the male protagonist. They live together in a rented house. The male protagonist is a musical genius. His deceased sister has the dream of appearing on the stage. The male protagonist disguises himself as a woman to participate in the competition for his sister. The female protagonist has always supported him, but as if the task is completed, she suddenly leaves without saying goodbye...