Despite his win, the victory is bittersweet. The blood loss is so extreme that Killua collapses, nearing death in the dark caves. His final thoughts drift toward Gon, apologizing for not being able to continue.
Because the darts only exist when they pierce the skin, they are impossible to block or dodge using standard reflexes. Hunter X Hunter 2011 Episode 101
Using his Godspeed (Kanmuru) lightning reflexes, he catches the final dart at the millisecond it materializes. Despite his win, the victory is bittersweet