Killua is a Transmuter type of Nen user, which means he can change the properties of his aura and make it mimic something entirely different, in his case, electricity. Killuas Nen abilities include Godspeed, which increases his speed in combat drastically by making use of his electrical aura, and Thunderbolt, a long-range attack. Killuas Nen abilities are a result of his exposure to electricity since early childhood, which allowed him to model his Nen ability after it.