Meet Kaito Takagi, your typical high schooler with a low profile. He spends his days exploring dungeons in Japan, hunting slimes for some extra cash. On the side, he quietly admires his childhood friend, the popular girl in class. One day, a rare golden slime shows up, and after Kaito defeats it, he finds a super valuable item—a card that can summon mythical beings! He decides to use it and summons a stunning warrior maiden. Now, Kaito has a chance to rise above his ordinary explorer life. Get ready for a modern fantasy story filled with battles! (Source: MAL News)

After an accident that killed his father and left his sister with a disability, Shun Tokinoya's mental duress has led to him refraining from online gaming. Now a model high school student who feels remorse over his past lifestyle, Shun works part-time in the cybercafe owned by his childhood friend Nozomi Inatsuki in order to support his family. Despite this, an incident pushes Shun back into the world of online gaming. Following the sudden retirement of all players of FOX ONE—Nozomi's father’s esports team—Shun learns that the Inatsuki family is in severe debt. In order to repay the money they owe, Shun reluctantly agrees to participate in an online game tournament: Xaxerion Championship. Joined by their classmate Akito Sendou, the three of them scout for talented players to rebuild the team. Although they are lucky to find two promising additions to FOX ONE, it is too soon to celebrate: if Shun does not let go of his guilty conscience, the makeshift team stands no chance at winning the tournament.

As technology advanced, humanity gradually colonized the entire solar system, occupying planetary facilities from Mercury to Pluto. This results in a large-scale athletic tournament, the "Daiundoukai," where several aspiring female athletes from all around the solar system compete. The winner of the tournament is crowned the "Cosmo Beauty," obtaining a queenlike status. When outgoing potato farmer Kanata Akehoshi was a child, she witnessed a meteor-like object falling from the sky, crashing in a nearby forest. When she came to investigate the wreckage, she saw a damaged spaceship and a girl who seemed to have been in it weakened by the impact. The girl gave Kanata two wristbands, alongside a request that Kanata join the Daiundoukai and become the Cosmo Beauty. Kanata obliged, but before she could ask for the girl's name, she mysteriously disappeared—leaving nothing,not even the crater caused by the crash. Since then, Kanata has devoted herself to training, aiming to fulfill her promise. After winning the qualifying round to represent the planet Earth, Kanata goes to the University Satellite—an institution where she and other candidates study to prepare themselves for the upcoming competition. There, she meets and befriends her fellow competitors, helping them get along with each other to perform better in the games. As Kanata grows closer to the coveted title, so do her chances of meeting the girl who changed her fate—and she discovers an underlying mystery behind the Daiundoukai along the way.