少女戦機 ソウルイーター

Based on an erotic game with the same name by Lune. Ryusuke is about to be kidnapped by Kimaira, but his older sister, Misa, saves him in exchange of herself. He decides to save Misa, and looks for his company, and meets Mikoto. She was also attacked by Kimaira and lost her family. At this very mome...