After inheriting the company from their parents, siblings Yuuhi and Yuamu Oudou have started to work at Ultraterrestrial Trouble Solutions, an organization that hunts aliens. Although they have never encountered aliens before, Yuuhi is desperate to meet one as he believes that an alien has stolen his important item called the "Earthdamar." One day, while searching for extraterrestrial creatures, Yuuhi and Yuamu find a strange spot in the forest where many trees have fallen, forming a scenery similar to a crop circle. As they venture further, they discover a mysterious spaceship and enter it out of curiosity. To their surprise, they come across Yudias Velgear, an alien from the Velgear Star Cluster. As it turns out, Yudias is seeking to learn about Rush Duel—a card game popular among elementary school students—as he believes that it will save his home from a long war. With the siblings agreeing to teach Yudias about Rush Duel, they eventually realize that their first contact with an alien may not be a random coincidence.

After waking from a long cryogenic sleep, high school student Akira Himegami finds himself in a world he no longer recognizes. The city lies in ruins from war, society is now governed by an organization called OWEL, and traditional marriage has been replaced by a new system known as "Elsie." As Akira struggles to comprehend this drastically changed future, a familiar figure appears before him—Yuugure, who bears a strong resemblance to his girlfriend Towasa. To his shock, Yuugure smiles gently and proposes: "Akira... please marry me." Confused by her sudden proposal, Akira agrees to travel with Yuugure, holding onto hope that somewhere in this world, the real Towasa is still alive. Along their journey, they encounter the evolving forms of love in this new era and reflect on what their bond truly means.

Following his legendary father-son battle against Yujiro Hanma, Baki faces a new threat: the resurrection of Japan's greatest swordsman, Miyamoto Musashi. As warriors like Doppo Orochi, Jack Hanma, and Kaoru Hanayama return to the fight, the stage is set for an unprecedented clash the strongest underground fighter vs. the legendary samurai, in a cross-era showdown.

Atsuko "Akko-chan" Kagami (known variously as "Stilly," "Caroline," or "Julie" in Western versions of the anime) is an energetic elementary school girl who has an affinity for mirrors. One day, her favorite mirror which was given to Akko by her mother (or in some versions, by her father, as a present from India) is broken, and she prefers to bury it in her yard rather than throw it to the trash can. In her dreams, she is contacted by a spirit (or in some cases the Queen of the Mirror Kingdom) who is moved that the little girl would treat the mirror so respectfully and not simply throw it away. Akko-chan is then given the gift of a magical mirror and taught an enchantment that will allow her to transform into anything she wishes.