Totteoki Maxion

From CPM: This great graphic novel tells the story of the love triangle of Yuichiro, a handsome teen, who finds himself swept away by the new student, mysterious blonde Shion, even as he tries to remain true his beautiful brunette girlfriend, Maki. When while on a student cruise, they're suddenly shipwrecked by a godlike supernatural, and Shion is revealed to be a charmed one herself!