Yuuhi and Yuamu Oudou have joined Ultraterrestrial Trouble Solutions, an organization that specializes in tracking down aliens, having inherited their family business. Yuuhi is excited to encounter an alien and reclaim his valuable "Earthdamar" item, which he believes was stolen by extraterrestrial life. During their quest, the siblings stumble upon a peculiar area in the woods, where fallen trees mimic crop circles. Their curiosity leads them to investigate further, revealing a mysterious spacecraft. Inside, they encounter Yudias Velgear, an alien from the Velgear Star Cluster, who is keen to learn about the popular card game, Rush Duel, to aid in his war efforts and protect his homeland. The Oudou siblings happily agree to teach Yudias about Rush Duel and quickly realize that their encounter with an alien may not have transpired by chance.