A kindhearted and sophisticated teenage boy. Kio is easily able to accept the proof that his new friend is an alien, and that both his other friends are secret agents. He knows how to handle firearms, though he is not sure what business his Uncle Yuichi is in to have them. He displays a strong sense of justice, and is willing to take action when he feels it is needed. This sense, and his treatment of others, draws the attention of his female friends. He is unsure about his reaction to all that interest, and their attention begins to cause complications for Kio. Eris the Catian in particular has decided that she wishes to be his mate as she is about to come into her first heat.
Oblivious to Love: Despite Eris spending the first half of the series literally and directly saying she likes him and wants to have sex with him, he seems to forget all about it the moment she stops being in heat.
A 16-year-old scout for the Catian people exploring Earth. Tall and well endowed, she has easily befriended many people, and regular cats she has met on Earth. Initially most do not believe her to be an alien, but she shows Kio the proof directly with her technology, ears and tail. While she is learning the ways of Earth, she is also a competent fighter who employs strategies and technologies not seen on Earth. Her interactions with Kio are closer and more emotional, potentially due to the fact she is 16 and about to enter her first heat. With the kindness and interest he has shown, she has selected him as a mate. Her first heat was forcibly ended by pills as it was causing disruption to her duties as an ambassador and representative of Catians on Earth. She develops feelings for Kio after she found out he risked his life to save her when she was captured
Pervert Revenge Mode: She can skirt the line between this and Unprovoked Pervert Payback when Kio sees her in unfortunate positions. Really, beating the guy up for walking into his own living room? Or coming running to help you after hearing gunfire in a public street?
Shipper on Deck: for Eris and Kio, though her methods are simply to arrange opportunities for them to spend time together, such as having Eris attend school with Kio, to give their relationship the opportunity to grow rather than any more forceful measures.
A Dogisian in charge of the underground relations between her home planet and governments through Earth. After knowing about the arrival of Catians on the planet, she devises schemes to prevent establishment of official diplomatic relations between them, including trying to eliminate Eris and her friends.
(light novels only) Jens' younger sister and Nirumea's most important staff officer. She's a brilliant analyst whose "active chart system" provides accurate predictions for future operations.
(light novels only) A warrant officer, superior to Ryunnu and (formerly) Jens. Having a senator within the Barunmuu world government as her father she had become spoiled and manupulative to obtain what ever she wants.
Despite the name, JACK is actually a woman. Her real name is: Janis Alectos Carotenas Karinato. She works for the CIA and is acting supervisor of Manami. She has noticeably long blond hair, is barely dressed and is often seen eating fast food, appearing to the stereotype of American women.
Kio's teacher and leader of Beautiful Contact Japan Sect. Due to the fact Elis doesn't represent the stereotypical alien (tentacles, green skin, etc), she firmly believes that Eris, despite the obvious, is not really an alien.
Reality Is Unrealistic: She believes this in this strongly, and as a result, feels that Eris isn't a true alien. In one episode, when Eris was trying to help out with the sci-fi film Kio's club wanted to shoot, everything they shot didn't look very realistic, which Ms. Itokazu was quick to point out. Not that anyone was paying attention to her though.
Crazy-Prepared: He usually seems to have a lot of things handy when the situation calls for it, such as a flashbang grenade when people were trying to attack Kio and Eris, and when Manami and Aoi needed a boat to rescue Kio and Eris, he happened to have one handy when his director coincidentally also needed it for his action movie.
Antonia Lirimonie Norfedras Papanorgas Arecroteles Cnorses Morfenoss is a wealthy 12 year old, leader of the Underside of Kitten Paw cult and rarely seen without wearing a pair of cat ears. She grows attached to Kio in the last episode due to him becoming a cat boy.
Bi the Way: possible, or it could just be due to her feline obsession.
AKA Black Amaryllis, an agent working for the British SIS. Comes from a former British aristocrat family at the age of 16.Born with a heart defect she had gone through a heart reconfiguration surgery that gave her super human abilities.