If I Don't Do It With My Brother, My Life Will Be Over?!

My older sister rejuvenated and became a high school girl again!? If she wants to return to her old self, she needs to have sex with me... My bashful sister is too sexy that I'm completely turned on now!! (Source: Coolmic) Note: Simultaneously released in long-strip and traditional formats, with 18 episodes and 6 chapters respectively.