Killua Zoldyck

Killua Zoldyck is a born killing machine. However, he's also incredibly loyal to his friends and does everything in his power to protect them. Killua is already quite strong when fans see him during the Hunter Exam arc, but he ultimately develops a magnificent stockpile of Nen abilities. His Godspeed, Whirlwind, and Speed of Lightning techniques allow him to move faster than most eyes can perceive, while simultaneously electrocuting his enemies. (he's only 12)