Tenshi ni Narumon!

I'm Gonna Be An Angel! (天使になるもんっ!, Tenshi ni Narumon!) is a Japanese anime produced by Studio Pierrot in 1999. A manga serialized by Monthly Ace Next was also released in Japan in 1999. The anime was formerly licensed for release in the United States by Synch-Point.

Plot
Yuusuke Kamoshita is a normal high school student living alone until he literally stumbles across a naked girl in a forest, a very energetic, yet innocent girl named Noelle. Before he can even fathom what's just happened, Yuusuke is inducted into Noelle's family of otherworldly beings who move into his tiny home replacing it with a huge plastic-looking castle and much that disrupt his life. All Yuusuke wanted was for his crush, the beautiful Natsumi Suzuhara, to notice his attention. But instead, Yuusuke's wish for Natsumi to be his angel becomes problematic with an angel-in-training following him wherever he goes, followed by interference with Silky and her minions interfere as the series goes on.