Easy, no NPCs appear in the show.
You guys seem to be a little confused about the hp regeneration thing, it's not a special skill Kirito has, this is a very stats heavy based game, so if he outlevels people too much, the damage they do to him doesn't reach the amount necessary to hurt him, since they are being too slow reducing his hp.
Ever tried to fight a level 90 PK in an MMO while you are lvl 30? This is the same thing, you can barely scratch him.
There are 10 unique skills in the game, one of them Kayaba Akihiko took for himself, though we never get to see the other 8 before the game ends.
Klein's "katana wielding", for example, is what people call a hidden skill, no one knows how it actually appears, but there's always some reasoning behind it.
He actually works really hard, grinding all night and beating high level dungeons all by himself.
For some reason this stuff never made it to the anime, along with another arc called "The first day". They also took out inner monologues, which explain a lot of game mechanics and explain most of the reasoning behind the characters actions.
A-1 is doing a really shitty work adapting this.
Post edited on 8th Oct 2012, 8:07pm