This thing disarms your taste in about nine minutes and then dares you to keep watching, and you do. Yuuya walks through his dead grandfather's door, punches a bear the size of a truck, comes back to Earth with abs and no glasses, and the show treats that as a complete character arc, because it is one. There's zero shame in it: Night the wolf pup as an accessory, Lexia and Luna competing for a boy who blushes at eye contact, Kaori and Yui and Ayano stacking up like DLC, the sports festival where he casually humiliates the kids who used to shove him. The writing is garbage and the worldbuilding is held together with tape, and the jokes still land because the anime knows exactly what it is and commits harder than shows with ten times the budget. It's the isekai equivalent of gas station fried chicken at 2am. You'll defend it to nobody and finish all 13 anyway.
Yuuya's life has been nothing but rejection. His classmates mock him. His parents ignore him. Everything changes when he inherits his grandfather's house and finds a mysterious door hidden inside. One step through it transports him to a sprawling magical realm brimming with dungeons, monsters, and incredible power-ups waiting to be claimed. He doesn't waste the opportunity. Yuuya grinds relentlessly, collecting skills and strength that feel impossible in this fantasy world. Then he returns to reality. Back on Earth, his newfound abilities make him unstoppable. The kid who once cowered in corners now commands respect through sheer capability. His former bullies watch in confusion as he transforms into someone they can't touch. But power alone won't fix what's broken inside him. As Yuuya rebuilds his confidence and reputation, he must figure out what the door really means for his future. Does he belong in the magical world or on Earth? The answer might require choosing between them.