Killua continues to bleed from his wounds sustained from Ikalgo's bullets, when he hears a tune in his head and his hand is suddenly pierced by a fish-shaped dart. He is again struck in the stomach, and his body dons the colors of a dartboard. He is unable to pinpoint the location of the attacks, and he begins hearing a voice in his head, which is the voice of the Ortho brother. As the attacks continue coming relentlessly, Killua realizes that he is the dartboard in a game of darts. The brother congratulates him on his realization, but adds that it is useless because the darts cannot be stopped whatsoever. He reveals that he is throwing at a dartboard whose segments are linked to various locations on Killua's body which are worth different points.
The siblings' ability is called Darts de Darts. It begins when a tag, created by the sister, is attached to target, which activates the game. The brother throws darts at the dartboard, and the larger fish dart appears on the target at the corresponding location. It cannot be dodged as the dart only exists once it touches the body. It comes with a heavy cost: if the brother misses the final shot, all the damage gets reflected back onto the siblings. However, the siblings have immense confidence in each other.