A kindhearted, yet sophisticated teenage boy, Kio is able to accept easily 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 isn't 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's 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 in to her first mating season.
In school, he's a member of the sci-fi movie club, and has a great interest in old movies.
In the end he's forced to turn himself into a Catian to restart the Catian mothership's sytems, due to the invalidity of his human DNA (though he turns himself back to a human not long after).