Having resolved the crisis in the Petrification Kingdom, Senkuu and his companions gear up to deal directly with the mastermind behind the petrification phenomenon—who supposedly resides on the moon. The ambitious spaceship project, however, requires immense manpower and critical resources scattered across the world. Thus, the Kingdom of Science exploration team kick-starts its transcontinental journey on the ship Perseus to gather them all. Equipped with modern technology and bolstered by the new, capable members in their ranks, the exploration team feels confident about setting sail to their first destination: America. They soon realize that the region now hosts adversaries controlling the resources they need, doing so with scientific technology which rivals and even exceeds their own. In a battle of science versus science, Senkuu and his team must outsmart their rivals if they are to have any chance of ensuring the continued survival and rejuvenation of humanity.

Since childhood, Kazuhiro Kitase has been able to dream of a different world. He can return to reality by falling asleep or dying, and he can pick up where he left off by sleeping again. For years, he has had many adventures alongside Mariabelle, a beautiful elf who works for the Sorcery Guild. On one of their escapades, they come across the lair of a dragon taking care of its eggs. They inadvertently wake the slumbering beast, who promptly reduces them to ashes. For Kazuhiro, it is merely a temporary setback, as he can simply go back. However, he is shocked to find Mariabelle herself safe and sound asleep next to him. Kazuhiro realizes that his dream world is an alternate reality altogether. In the meantime, he makes the most of this bizarre circumstance, introducing Mariabelle to the sights and wonders of Japan. Now, with their time together spanning two worlds, their real adventures have just begun!

Alina Clover becomes an adventurers' guild receptionist, believing that—unlike the adventurers who risk their lives every day to conquer dungeons—she will enjoy a safe and comfortable career with plenty of benefits. She hates overtime work more than anything, longing for the day when she can finally clock out on time. Sadly, that day has yet to come, as she must constantly trudge through piles upon piles of paperwork. To make matters worse, when adventurers take too long to subjugate a dungeon boss, the backlog only grows, forcing Alina into even more overtime. Whenever her patience runs thin, she dons a disguise and takes care of the boss herself, soon gaining infamy as the enigmatic "Executioner." Alina has managed to keep this secret for two years—until she finishes off a boss assigned to the high-ranking party Silver Sword. Unfortunately for her, the party's eagle-eyed leader, Jade Scrade, deduces her identity, jeopardizing the receptionist's dream of a carefree life.