Carefree, popular Yuki is in for a surprise on his 17th birthday. His parents have chosen that day to tell him that his father is a space alien and, therefore, he is half-alien. As a half-alien, he has the ability to change his form. For example, he can change himself to look like a younger version of his human mom.

His father also explains to him that some aliens on earth have less than friendly intentions, and that he should help protect Earthlings from them. Will Yuki be able to keep this a secret and continue his happy school days with his friends Shinichi and Midori? On an even stranger note, will he be able to keep Shinichi from falling in love with him while he's transformed into a younger form of his mother?