A Romance of the Three Kingdoms retelling using SD Gundams.

Life seems simple for Koichi, a young student, until he learns that he is the reincarnation of an alien protector who crashed onto the mantle of responsibility as"defender of the Earth", Koichi/Babel teams up with a trio of super-powered alien companions to battle the the dark forces of an evil cult leader. The war to save humanity takes Babel from the deserts of southern Asia to the upper east side of Manhattan and ultimately to a final showdown with "the master" in a hidden base nestled in the Swiss Alps. The action is fast-paced and deadly. The fate of the world rests in the ability of this courageous youth to tame his latent psychic power and use it to defeat the enemies of mankind. (Source: AnimeNfo)

Yusuke, an orphan, literally has Rouge, the amnesiac oldest daughter of the Underworld's deposed royal family, fall out of the sky into his lap. She is soon followed by her two younger sisters and also their family's enemies. Rouge must decide if she wants her memory to return, while Yusuke must deal with the upheavals in his life the Princesses have caused.

Part II of Sword Gai: The Animation.