After a lifetime of relentless bullying, neglect from his parents, and being treated as an outcast by his own family, the overweight and shy middle school student Yuya Tenjo inherits the home of his recently deceased grandfather, the only person who ever showed him kindness. When his family abandons him to live there alone, Yuya discovers a hidden door that leads to a mysterious and magical other world called Arselia. Inside, he finds the residence of a legendary sage who has long since passed away, along with powerful weapons and rare treasures. By defeating a formidable monster on the property, Yuya gains immense cheat-like skills and levels up in a manner akin to a video game.

The most significant change occurs when he returns to Earth; the effects of his leveling up follow him, radically transforming his physical appearance into that of a tall, handsome, and athletic young man. Yuya begins living a double life, using his newfound power, wealth, and artifacts to improve his situation in the real world while continuing to explore and grow stronger in the other world. On Earth, he catches the attention of Kaori Hojo, the wealthy and kind "princess" of the prestigious Osei Academy, who invites him to attend her school. In the other world, he rescues Lexia von Arselia, a headstrong half-elf princess who quickly becomes infatuated with him, as well as Luna, a skilled but dangerous former assassin. These characters eventually discover his secret, with Kaori being the first to join him on his interdimensional adventures and Lexia even enrolling at Osei Academy to remain close to him.

The television special, scheduled for broadcast at the end of March 2026, continues this narrative by adapting material from the fifth volume of the original light novel series. The story introduces new characters to the conflict, including Gilbert, Oma, and Yuty, a character who appears in a school uniform. The special brings Yuya, Kaori, and Lexia face to face with a powerful new adversary known as Ken Sei, or the Fist Saint. As Yuya continues to navigate his parallel lives, balancing school life and friendships with the growing dangers of the other world, this special episode presents a significant new challenge that tests the bonds between the main characters and pushes Yuya to unlock even greater potential from his cheat skills.