When I say it doesn't hurt me,

Nen is the ability to manipulate one's own life energy or aura and grants the user paranormal abilities. There are many different types of Nen that one can master and Killua has mastered the four basic techniques of Ten, Zetsu, Ren, and Hatsu - and at least five of the advanced techniques Gyo, Shu, Ko, Ken, Ryu.

Beyond that, Killua has a natural affinity for being a Transmuter, which allows him to change the properties of his aura to mimic electricity. He has honed abilities in two other affinities, Enhancement and Conjuration. Enhancer allows him to strengthen and increase the natural abilities found within himself such as his strength and speed. While Conjurer allows him to create an item out of his aura. Since he was born with the Transmuter affinity, he will never be able to master any of the other affinities completely.

Killua can wield his twin yo-yos in combination with his Transmuter abilities and turn them into electric weapons. This may not cause damage, but does hurt and stuns opponents. He must "charge" himself after using too much of his electrical aura, mostly by the means of experiencing a shock himself from a taser or outlet. It does run out quickly as he isn't always aware of how much power he's outputing. The electrical aura can be used to power machines or burn/burn out common items and machines.

The most basic of attacks that allows him to simply shock people with a touch of his hands. It will hurt and stun opponents for a few moments.

A bolt of lightning that he can aim at opponents that can leave them paralyzed for a bit and causes pain, leaving them open to another attack.

The peak of Killua's Nen abilities, which requires him to go through the stages below. It pushes him past the limits of his physical potential to make him faster, stronger, and more agile. He can decide how much voltage someone touching him will feel, such as a friend or ally only receiving the smallest of shocks or an enemy the highest voltage. It has two core functions, one for fighting and another for sheer speed.

⚡whirlwind This puts him in a state where he automatically reacts to outside stimuli. He sends electrical signals to his muscles to react and act without relying on "orders" going through his brain and slow nervous system. It can be programmed and reprogrammed to whatever Killua is facing - whether it be an enemy or friend, which means it has both offensive and defensive abilities. It makes him move faster than a brain or body can process information in most cases.

⚡speed of lightning This is the stage of Godspeed that allows him to remain in control of himself fully, so it's not used as much in battle. Rather it's used to cover long distances in a short amount of time. Due to the fact that speed is key here, Killua is more affected by the terrain which can slow him down. If on uneven or unfavorable terrain, his estimated speed is about 240km/h (about 149.1 mph), meaning he could reach even faster speeds on a road or flat terrain. Should he be carrying someone while in this state, they will experience small electric shocks so long as they are in physical contact with him.