Naruto HunterxHunter Fanfic
A 13 year-old Killua Zoldyck's aniki, Illumi, commits murder in the village of Konohagakure. Illumi escapes, but on Killua's way to stop his brother, he gets caught by Hidden Leaf ninja. Taken back to the village, people are suspicious of him and nobody trusts him either. They don't sense much from him, but something is definitely off. By the Hokage's wishes, Killua joins Kakashi's team seven, as a temporary member. But Killua knows that he must get back to his lands, to get back to his younger sister, and to his best friend Gon-- and to stop his brother.
*this is when Killua has his electric nen abilities, and is a pro Hunter and when Team 7 is 12/13*