✦The series that mainstreamed the 'trapped in a game' isekai wave, a lightning rod that shaped (and divided) the whole genre.
Synopsis
Ten thousand players enter a new full-dive fantasy game on launch day. The logout command is missing. Their host eventually explains that death in the game will also kill the person wearing the headset. Clearing the floating castle is now the only exit. Tutorials acquire unusual urgency, and experienced beta tester Kirito discovers that knowing the map does not make him popular.
Log in on launch day. Discover the missing exit. Hear the creator announce one path home: clear the castle. Death inside means death outside. Kirito knows the early floors from testing. Everyone else knows he knows. Information becomes essential equipment.
The town square fills with players who think launch day is a party. Then the sky changes while the logout button stays gone. The rules become terrifyingly physical. I was locked in before the first fight. Kirito knows enough to move, but not enough to make the crowd trust him. A familiar game interface suddenly feels like the walls of a real place!
The lone expert hero is obvious power-fantasy material. The opening at least makes his advantage socially costly. Kirito knows routes that other players do not, while everyone has reason to distrust the people who tested the game first. The strongest part of the premise is logistical. A launch-day crowd must turn a hostile interface into somewhere survivable.