What would you do to save someone you love? All brothers Shoma and Kanba know is that, after collapsing in an aquarium and apparently dying, their terminally ill sister Himari was somehow revived by a Penguin hat that she had wished for. Now they're on an impossible mission, because the price of keeping Himari alive is to find a mysterious object called the Penguindrum, and they'll do anything to save their sister. Anything. As they travel separate paths in their search, they'll have to unravel complex riddles, make alliances with strangers they know they shouldn't trust, and question the very fabrics of time and destiny.

A terminally ill girl named Himari Takakura is miraculously saved from death by a strange spirit who resides in a penguin-shaped hat. However, in exchange for extending her life, the spirit tasks Himari's brothers, Kanba and Shōma, to seek out an elusive item known as the Penguin Drum with assistance from a trio of strange penguins.

Sato's life – or what's left of it – is a paranoid mess of conspiracy theories and social anxieties. He's terrified of the outside world; his apartment is overflowing with the remnants of cheap take-out food; and his retinas have been permanently scarred by a steady diet of internet porn. But maybe it's not all his fault. After all, the nefarious N.H.K. is out there, and they’re determined to turn society's fringe-dwellers into a brainwashed lot of jobless, hopeless, futureless recluses. Enter Misaki – a mysterious girl-next-door type who is Sato's last chance to beat-down his inner demons and venture out into the light of day. She's ready to help him overcome his crippling phobias, but Sato would rather cower in his existential foxhole and pretend to work on the demo for his virtual sex game. He’s afraid to face the world. She's strangely desperate to fix a total stranger. Maybe together they can be normal.