Afraid that his life may end at any moment, Otto Suwen begins writing a diary documenting all of his experiences. Now part of Subaru Natsuki's eccentric band of colorful characters, the apprehensive merchant is certain that new dangers lie ahead in their mission at Sanctuary. But amid the rising tensions, there are still moments of respite and reflection, ripe with opportunities to make vivid memories.

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.

Determined to pursue his glorious childhood dreams, 30-year-old Rick Gladiatol, a modest clerk in the adventurers' guild, is offered a once-in-a-lifetime opportunity after he fatefully encounters the dark elf Reanette Elfelt. Reanette happens to be an elite adventurer of the legendary party Orichalcum Fist, whose members welcome Rick under the condition that he follow a Spartan training. Two years later, Rick is finally ready to take the E-Rank exam officially qualifying him as an adventurer. However, raw magical power can only be developed until one turns 20. As such, Rick faces the general hostility of fellow participants and examiners alike, leaving him no choice but to show the world that his hellish training has turned him into an invincible warrior.