Nyuunyuu

One day, Shoji Oba asks the woman posing as his sister who she really is. Her name is Erika Chichiski. She is a boob alien from the planet Boob. A meteorite hit her planet and broke it into pieces. She escaped and roamed about space before she came to earth. Shoji doesn't really believe her story, but he gives in to the temptation of having a big breasted chic around and decides to let her stay. However, Shoji soon regrets his decision

Erika is really a mad scientist, who starts creating strange creatures using advanced technology from the planet Boob. People around Shoji begin to panic. What will be waiting for us? This game contains both a love story and a slapstick comedy. Shoji's girlfriend, Marimo Kawai, has a warm personality and really makes him happy. However, Erika's big boobs embarrass her. Inaho Watanabe, who grew up with Shoji, is beautiful, smart, and also very rich. Wakaba, Shoji's sister, is reliable and does most of the housework. Players will be able to enjoy sex with girls with big boobs. If you're a big boob lover, this game is for you!

[From gamelexgs]