Wisteria is an orphan girl living in a corner of the British Empire at the end of the 19th century. Her life is desolate and bleak–until she encounters Marbas, a powerful but equally lonely immortal being with a furry appearance, hounded by hunters. Together, Wisteria and Marbas roam the Empire–populated by humans and human-like beasts–in search of a place where they can live together in peace.

The happy-go-lucky Michi Sonoda announces to her teammate, Sanae Takigawa, that she will quit judo for good after her final middle school tournament. This leaves Sanae in disbelief; after all, it was Michi's passion toward the sport that reeled Sanae into judo in the first place. Michi claims that a well-spent youth should be associated with things such as getting a boyfriend rather than sweaty tatami mats. However, Michi's plan to end her fledgling judo career with a bang is spoiled after experiencing an embarrassing defeat at the hands of the talented Towa Hiura. Later, her plan is further derailed when she finds out that Towa has enrolled in the same high school as herself and Sanae. With the sudden appearance of her past foe, Michi may soon realize that she still has lingering feelings for the sport of judo.

Kaname Okiura, a student of Prefectoral Umineko Shougyou High ("Umishou" for short), joined the school's swimming club in order to learn how to swim, but the club is filled with weirdos, let alone who can teach him swimming. Then, a sunny, happy-go-lucky girl named Amuro Ninagawa who transferred from Okinawa joined the club. Her extraordinary underwater speed and unorthodox swimming style (plus her personal habit of nude swimming—a powerful magnet to teenage boys) surprised every club member, especially Okiura, because she reminds him of a mermaid-like creature he saw only once in his early childhood.

When aliens known as the Oni threaten to invade the Earth, they promise to leave under one condition—a randomly-chosen human must win a one-on-one game of tag against Lum, the beautiful daughter of the Oni leader. The "lucky" person selected happens to be the lustful and unlucky high schooler Ataru Moroboshi. Given 10 days to attempt to grab Lum's horns, Ataru realizes how impossible the challenge is as he is faced with Lum's extraterrestrial powers. Motivated by a promise of marriage from his childhood friend Shinobu Miyake, Ataru manages to catch Lum off guard. He mistakenly grabs hold of her bikini top first, but he eventually achieves his true goal. Although the game is over, Lum misunderstands that she is the one whom Ataru wants to marry, and she decides to move in with him. The poor student constantly tries to shake off the clingy Lum while doing his best to reconcile with his desired fiancée. After Ataru's heroic feat results in such a disastrous outcome, it is questionable whether luck will ever be on his side.