My Sister Guide

What is the greatest sorrow of being a sister-in-law? That means being an only child and having no biological sister to control! A flying saucer fell from the sky and destroyed the family's house. Then he was possessed by a goddess Loli and a system was forcibly installed. The homeless protagonist ushered in the greatest luck in eighteen years, moving to his father's colleague's house to live with two beautiful girls. While the protagonist is growing up with the help of the system, the whole world is also changing bit by bit under the influence of an evil force...