Kono Sekai wa Fukanzen Sugiru

Oh no! The characters are all trapped in a videogame medieval fantasy world! This is such an unique plot! Following a somewhat similar plot, SAO and Kono Sekai wa Fukanzen Sugiru take the now-rather-common concept of "fully immersive virtual reality RPG" games and traps its protagonist and the rest of the characters in their respective worlds, forcing them to find a way out as they play quite literally a high-stakes game. Both anime have a lot of "gamer" lingo and have, to different extents, their characters abuse the games' systems to their advantage. 

Two anime which, although ultimately quite different in the way they develop their arguments, follow a similar plot: our protagonist is trapped in a fictional, medieval fantasy virtual reality world, and after meeting a certain NPC character, they embark in a journey as they try to find a way to get out. The way both anime play around with the virtual, programmed realities draws some similarity, as well as with the occasional gore, the realistic NPCs and the world which feels rather alive for a virtual one. 

They have similar atmosphere. Dragons are problems in both series and the main cast consists of a man who is knowledgeable about monsters and other characters who specialize in other fields. The adventure is light-hearted and filled wifh humor.