MUDR-204 My Sister Was The Greatest Sidekick Aoi Amano Rina Takase

My younger sister saw me masturbating in my younger sister's eroge. My younger sister, who always has a straight face, then somehow ends up helping me with my masturbation. ? And why am I still watching my sister masturbate!? Super topical work depicting the perverted relationship between a brother and his sister who won first place on FANZA and was only able to get out of it with his sister.