Keroro Gunsou

A frog-like alien arrives on Earth to carry out a mission of conquest, but after his identity is discovered, he is left behind by his unit and taken in by a family. He is assigned to perform domestic tasks and lives in a basement believed to have once been a prison haunted by a girl's spirit. In his spare time, he builds model kits. While living with the family, he reconnects with other members of his team who were also left behind during the mission.