Guardian Hearts(2001)

Guardian Hearts

Kazuya is a normal guy who discovers the secret identity of a space alien named Hina, who comes from the Planet of Light. She is a member of the Guardian Hearts--well, to be exact, Hina is a Guardian Hearts dropout, and she is assigned to protect earth as a last chance at redemption. When Kazuya finds out Hina's secret identity, her mission may be over before it has a chance to begin. That is, unless a crazy little thing called love gets in the way!

(Source: VIZ Media)