The Hunter Exam is a pretty much a meet cute. Gon and Killua hit it off immediately. The narrative has them finishing their race at the same time as something straight from a Shojo. This is even worse in 1999 because Killua fully looks across the room to see Gon. Adding on the Zoldyck arc is pretty much a version of “Forbidden Love” trope. Which look at Tanabata and it makes sense.
The fact that Togashi canonically loves playing around with Queer Themes and an enjoyer of BL (So much he tried to do one that got canceled). And this clearly shows in characters such as Alluka, Pitou, and Pouf. I also will include Kurapika in this because he’s atleast gender non confirming. (So much half the time people think he’s a woman first meeting him when they first watched the anime)
The fact that Togashi is married to Queen Yuri herself, Naoko Takeuchi who notoriously had two canon lesbians (Sailor Uranus and Sailor Neptune) be censored to be cousins in the English dub. And the fact the main character Usagi Tsukino is very much implied to be a bisexual disaster with half her crushes not being cisgender men. This to say, he has Queen of the Lesbian army in his ear and we know the reason why Pitou slowly started to become so pretty is because of her.
The fact that Killua Birthday is Tanabata. One of the most romantic Japanese holidays. To explain for those unaware Tanabata is both two deities (Orihime and Hikoboshi) symbolized by the two stars, Vega and Altair. The legend in short is the Milky Way separates these two lovers and so they can only meet once a year. If you know the legend in length, you can notice that Killua is clearly supposed to be Orihime in this situation. Especially in the legend it’s her father that caused them to separate because she wouldn’t do what he wants. This relates how Killua is forced to separate from Gon because of the Zoldyck family (Illumi and Silva as examples, which is why I think Gon is definitely gonna eventually get involved with the fact that Killua and Alluka are still running away from their family)
That Killua and Gon are compatible as Transmuters and Enhancers. And similarly their zodiacs are compatible (Being a Taurus and Cancer). Even their blood types are compatible.
That the whole Whale Island stargazing session was technically a campfire confession. (It wasn’t just strictly confession of love, it was a confession of what exactly what both want to do with reiterating how important each other are to eachother.) Adding on star imagery occurs a lot with them again connecting to Killua birthday date.
The fact that they canonically flirted and kissed in Hunterpedia. Not strictly canon but you can see the producers clearly saw the subtext that was already there. Including the Love Umbrella.
The fact again relating to Tanabata, they are both shown numerous times to do anything for the other (Examples: Nobunaga and The Dodgeball Game). They are doing all sorts of soulmate behavior. They are yin and yang. One can’t have their arc without the other etc.
The fact that canonically the Kiriko think Killua smells like Gon. That actually happened. During the same period Gon was wanting Killua to come back as soon as possible. The infamous “Killua is the only one for me” which with Japanese context is very romantic actually.
The whole Rainbow Gay Diamond that got censored to hell and back that Killua gave Gon in Greed Island. The fact that Killua is so important to Gon he wanted to introduce him to Ging. Or the fact Gon reaffirmed his friendship with Killua by thanking him again in Greed Island. Greed Island was really gay.
Numerous times Killua gay stares at Gon especially during the Chimera Ants Arc. This to say Gon isn’t also gay staring at Killua, Killua is just on a level of yearning thought impossible by scientists of our era.
Killua saying Gon is Light making the homophobic dude bros sadly accept that Killua is just homosexual. That Killua is gay. The fact numerous relationships in Chimera Ants Arc are mirrors for Killua and Gon (Mererum and Komugi/Palm and Knov/Even Pokkle and Ponzu)
The Fact Palm said about how love can come out of nowhere is supposed to sorta put emphasis that Killua is feeling more than platonic about Gon. With his OH moment being in that dialogue in Greed Island.
Killua crash out is pretty much wanting to stay by Gon side forever which is very much shown in a jealous tone when he is stalking Palm and Gon date. Pretty much acting like a gay kid thinking he’s crush will leave him once he gets interested in girls.
Not strictly canon but also very much jealous of Retz that he sorta tried to kill himself? It was mainly wanting to help Gon that gave Killua the strength to rip out the needle out of his head. Which is clearly an allegory for internalized homophobia that had him “running away” from Gon despite his feelings.
The fact the word used was Shinju which translated usually means Lovers Suicide. It isn’t always been romantically but dying together as a couple is sorta been romanticized in old Japanese poetry. (And the fact that their mirror duo does do a lovers suicide)
Nagareboshi Kirari is a song all about Killua and Gon relationship and it’s actually very romantic (also generally the 1999 opening is very gay and romantic as well. I’m just gonna post some translated lyrics. “I think of you, even when we’re far apart Alone, looking up to the sky beyond like this believing that we can one day connect our hearts Our meeting, crossing time, is like a dream Feelings, so many that I can’t hide them, dance in the wind If only I had a little bit more courage “ Like straight up this is just Killua thinking romantically. This is also not helped how Gon was literally on Killua mind and again Star Imagery because of Tanabata.
Some notable preview lines such as: We are connected by an invisible line, May we always be together, Hey what do you want to want to be in your next life? IN MY NEXT LIFE I WANT TO BE ME AND MET YOU AGAIN. Also adding here the numerous and countless times both Gon and Killua blush around each other (Gon mainly does so in the manga.)
Palm only regained her sense because of the nth Gay Crashout Killua had about Gon (which fair he was watching Gon try to kill himself) and she even said it was Killua who Gon needed the most. Generally the fact that everyone and their mother comments on Killua and Gon Greed Island and Upwards. Literally even fucking Hisoka called Gon “Killuas beloved”
That the whole separation in the 2011 is literally framed as a separation of lovers pretty much even with sad music and close ups and clips of memories. And the way they both had bittersweet eyes forcing them to separate. THE FACT GING KNOWS EVERYTHING ABOUT KILLUA BECAUSE GON CANONICALLY TALKED ABOUT HIM. That one of the animators I think drew romantic Killua and Gon? The fact as well the Japanese voice actors ship them as well. Killua VA even fully thinks Killua Loves Gon. And this is just what I got off the top of my head I’m probably missing some lmfao.