Mawaru Penguindrum

Brothers Kanba and Shouma adore their terminally ill little sister, Himari, and aren't prepared to lose her. They're definitely not prepared for a family trip to the aquarium, source of many of Himari's fondest memories, to suddenly turn tragic when Himari collapses and dies. What happens next, however, is beyond the siblings' wildest imaginations—as Himari miraculously returns from the dead, sporting a penguin-shaped hat, and accompanied by some magical new friends!

(Source: Seven Seas Entertainment)