This Ugly Yet Beautiful World (この醜くも美しい世界 Kono minikuku mo Utsukushii Sekai) is an anime and manga series by Gainax, by the same staff team that worked on Mahoromatic. It deals with the mass extinctions that have occurred on Earth in the past. It takes this subject and shows a very interesting possibility for how it might happen today, if the basics of the story are to be believed. In doing this it touches at the love we show for others in different forms, from boyfriend-girlfriend to the love within our families. Due to this more or less constant push on relationships, this anime fits best in the moe (cute girls, romance) genre.

Two young high school boys, Takeru and Ryo, are struggling through teenage angst when a mysterious light in the woods offers forth a young girl practically out of Takeru's dreams. They are promptly attacked by a strange alien-looking monster, which is defeated when Takeru mysteriously and spontaneously transforms into a powerful and strange looking beast himself. Not much is clear about the girl, who they name Hikari (Light), but she is more than a little bit strange. Without a memory or a past, the girl is integrated into the lives of the two boys and their families. She knows only her love for Takeru. Most of the group live in a type of group home, along with Jennifer Portman, a drunken American super-scientist who can't keep her hands off the boys and has her own theories about what Hikari is. The series follows them as they hang-out, go to school, and take trips, and all the while Hikari, and also later her "sister" Akari, learn about the human condition. They are also joined by a shape-shifting robot called Ioneos, apparently loyal to Hikari, and Kuon, a little floating alien. They also encounter more strange monsters on occasion. The series spirals towards a rather unexpected climax questioning the value of human life, relationships, love, and the spirit of survival shown by all life on Earth.

From Wikipedia