Killugon

Killugon is the slash ship between Killua Zoldyck and Gon Freecss from the Hunter x Hunter fandom.

Canon
Most of the series follows Killua and Gon's adventures together. They are one another's first friends, and develop the most next to one another. Killua also uses a lot of romantic language when he talks about Gon. They get the largest relationship developments during the Chimera Ant Arc.

- Hunter Exam

Killua and Gon first meet when they take the Hunter Exam together, and grow into fast friends because they are the only two who are the same age. This is interrupted when Illumi, Killua's brother, tells Killua at the end of the final part of the exam that someone like Killua has nothing he wants and should return home. Killua states that his largest desire is to be friends with Gon, and Illumi interjects that his desire is really to kill Gon, not befriend him. Leorio, Gon and Killua's mutual friend, interrupts this to say that Gon and Killua are already friends regardless of what Illumi says. Either way, the impact of Illumi's words is devastating for Killua and he returns home.

Gon, who has been unconscious for these events, wakes up and decides he immediately has to get Killua back. He confronts Illumi about what happened, tells him he's a horrible brother and (unknowingly) breaks his arm during the confrontation. Gon and Killua's mutual friends accompany him when he goes to Killua's family's mansion to get him back. There, Gon undergoes a lot of tests of endurance and pain to get Killua back. He succeeds, and a depressed Killua cheers up to hear Gon came up for him. Killua tells his father all about Gon, and he gets permission to leave with him.

- Heavens Arena

After they leave the Zoldyck mansion, they decide to train together in Heavens Arena. During this arc Killua expresses his admiration for Gon, and admits to Wing, their mentor, that he and Gon are a bit similar in their recklessness. Killua asks if its okay if he can visit Gon's home with him. Gon agrees. One night while starwatching, Gon confesses to Killua that he's his first friend. Killua admits the same is true for him. Gon says he always has fun when him and Killua are together, and asks if he wants to stay with him while he tries to find his dad. Bashfully, Killua agrees.

- Yorknew

During a reconnaissance mission they get captured. Killua offers to take on the enemy alone (and die) so Gon can get away, but Gon hits him on the head and says he can't say things like that. Killua points out Gon's hypocrisy, because Gon often says things like that. Gon replies "I'm allowed to but you aren't!" They both manage to escape after.

- Greed Island

Gon expresses concern for Killua multiple times after a spell is cast on him. They meet a new mentor, Biscuit, and she comments herself that they 'make a great team'.

Fanon
The ship has been the most popular in the HxH fandom since the manga started publishing in the 90s.

Togashi, the mangaka, has written multiple LGBT characters in the past which gives some precedence to believe it may be made canon by the end of the series.

During the Heaven's Arena arc, Hisoka (a transmuter nen user) says that 'Gon and him have good compatibility' because Gon is an enhancer, and Hisoka is a transmuter. It's often thought this dialogue is purposefully also referring to Gon and Killua, since Killua is also a transmuter.

Fandom
AO3

Trivia

 * There are multiple nods to the ship in canon, such as the HxH 2011 adaptation including their ship name under a romantic umbrella (the same as drawing a heart around a pair of names)
 * During the Yorknew Hunterpedia additions in HxH 2011, a kiss is added