IENF-087 I got aroused by my little sister's defenseless ass and kept fucking her from behind, making her pregnant

My parents remarried and suddenly I got a stepsister. She's honest, cheerful, and even though she's younger than me, she gets along well with me. She's a good kid, but her defenselessly cute ass is constantly being shown to me unconsciously every day... To be honest, she's exactly my type of stepsister. But doing something like that to family is unthinkable!! I've been struggling with this, and one day I finally reached my limit...