the hxh core four have not been together for some time and probably only spent a month around each other max so it might be difficult to understand why those relationships impacted them so profoundly but we must understand that before anything, that was the first time the four of them had ever really been Seen. that growth and love they shared, however temporary, is the beating heart of the story. their lives were renewed together and nothing can change that the foundation of the lives they live are owed to one another. they almost all become hunters together, start their new lives and journeys together.
gon, kurapika, killua, and leorioās most striking shared character trait is Loneliness. that and loss. the loss of friends, childhoods, parents, and in kurapikaās case an entire civilization. itās the Lack Of. the lack of personhood for killua and gon, money for leorio, a home for kurapika, the feeling of being Understood for all of them. itās these empty crevices and a longing for something to fill them that creates the trajectory for their friendships and respective character arcs.
they all find both themselves and what they desire in one another. kurapika sees himself in gon and killua, but he also sees his lost innocence and dead best friend in them. he sees in leorio the proof of goodness heās been searching for and the doctor for whom his search was cut short. kurapika is clearly very inspired by the endurance and strength of his friends and what theyāre able to manage throughout the hunterās exam and can remember his own endurance after losing everything he knew. he sees leorioās mourning for his friend transform not into rage but into hope.
leorio seeks money, but he also seeks proof of the possibility of a better world. he sees in gon and killua that such a thing can exist. gon, killua, and kurapika are all the sort of struggling people leorio wants to help. killua and gon show these older boys their lost youth but also that struggles can be overcome (particularly killua, who meets kurapika as a ruthless killer and who is soon trying to keep kurapika from going down the same road of loneliness and death killua has been on his whole life). leorio sees the cost of selfishness and not living up to his principles when he realizes how little attention heād paid to gon and killua while in medical school and the suffering they were going through that he had no clue about. and so his goal is reinvigorated; save his friends no matter the effort it takes.
gon starts the search for his father to fill that gap of loneliness, to find someone he thinks could understand or explain his recklessness, but as ging himself tells us, gon found much closer and more important relationships with killua, leorio, and kurapika. leorio provides a care for gon typically expected from a father or older brother that he has not received. though it backfires kurapika gives gon the encouragement he longs for and an understanding of how to use his power. and in killua, he can finally be understood not by an idealized concept, but by a living, breathing boy and the two of them can actually be kids together. killua can finally work through what it is to love and want and become someone at gonās side. people call leorio and kurapika killuaās āfriend in lawā but in leorio, killua can also see a kinder older man actually interested in his well being. and while he and kurapika donāt exactly get along, i think kurapika existing as an example of who killua doesnāt want himself or gon to end up as is important in its own way.
killua and gonās narratives compliment kurapikaās very well. killuaās introduction has him framed as a lying assassin who believes kurapika is only interested in revenge, but by the end of his arc heās probably the most honest about his emotions in the main cast, and wants to live a life based not in murder but in exploring himself healing (with alluka/nanika as a literal healer by his side). gon on the other hand insists kurapikaās care for his friends shows his primary goal doesnāt just need to be revenge, but itās gon who attempts to destroy himself for revenge using the same rules of sacrificial nen he first saw with kurapika. but gon is, of course, saved by killuaās loyalty to him in the end. it raises questions about how kurapikaāwith an arc very similar to gonāsāwill conclude his story. he is actively shortening his life for his revenge; will something be able to save him? will he lose his life as gon almost did?
together or not, these four charactersā narratives fundamentally revolve around one another (with eventually characters like chrollo, meruem, bisky, alluka, etc getting looped into the thematic throughline being constructed). itās not the amount of time that matters the most but the impact said time had. in just a few weeks, theyāre all shown new sources of inspiration, and possibilities they hadnāt considered for years are opened right before their eyes. characters who have experienced so much cruelty whether at the hands of systems or individuals finally see the existence of so much kindness. this time together was so important that kurapika, despite not seeing killua and gon since the yorknew arc (or about 25 years in real time, and about two years in canon) still thinks of them as a source of warmth that complicates his motivations for revenge. and itās of course that warmth that makes him believe he must push them away, as gon did to killua, so they are not witnesses to his self destruction.
as an aside i love how stubborn all of them are. these four characters arenāt exactly a unity of opposites as much as variants of one another all attempting to bring out the best in each other despite the complications.