On (怨, Malice) is one of the defining features of the movie Hunter × Hunter: The Last Mission. It is the opposite of Nen. Instead of utilizing life energy, the aura from On is derived from hatred and can be considered "death energy." It grants one immense strength, but will kill the user following their defeat. Jed, Gaki, Shura, and Rengoku are all users of On in the film.
Trivia
- It's interesting to note that the Kanji used for "On" is the same superimposed onto Gon and Killua the first time they felt Neferpitou's aura. This has led some fans to speculate that Neferpitou is a user of "On."