Sword Art Online
This is about millions of people that get stuck in a virtual reality game, sword art online. They can't log out, and if they die in the game, they die in real life. There is a dungeon with 100 floors. The only way out of the game is to defeat the boss on floor 100. The main character, Kazuto, but in the game his name is Kirito, is a solo player. He ends up partnering with someone named Asuna. They go through a lot of fights and sometimes almost death. This is a romance, but it's also sad. There is a season 2 called Gun Gale Online, and a season 3 that just recently came out. This is a good anime you should watch.