He is Hibari's right-hand man both in the present and future. Kusakabe highly respect Hibari and is very loyal towards Hibari and would diligently carry out his order whatever it would be without further question. He would always follow him everywhere to watch over him and make sure he won't do anything reckless, though sometimes this ends up with him being beaten by the latter. Hibari shows little care for Kusakabe's well-being, punishing him whenever he fails his duty as disciplinary committee despite Kusakabe already being injured and treat him indifferently as he does to others. However, they are shown to have a closer relationship in the future, as Kusakabe addresses Hibari by the nickname 'Kyo-san' and Hibari addresses Kusakabe with the nickname 'Tetsu'.
Hibari displays bitter resentment and rivalry towards Mukuro Rokudo due to humiliation over his defeat. As such Hibari appears to have developed an obsession to defeat Mukuro and from this, a hate for all illusionists. Reborn is even able to quell Hibari's rage by using the possibility of him fighting Mukuro again. Mukuro seems to have some interest in Hibari, after he was able to move with so many injuries. He even has his subordinates Ken, Chikusa, and Chrome to watch his match against Gola Moska. In the future, they still continue with this rivalry and have yet to finish (since Mukuro is still imprisoned). However, they seem at least, to have a respect towards each other, Mukuro even sent a map of Merone Base to Hibari when he disguised himself as Byakuran's subordinate. Ironically, both are totally in sync when fighting together as pointed by Reborn.
In the Databook, he commented that he can't understand Tsuna because Tsuna's weak sometimes and strong sometimes (Dying Will Mode). At first, Tsuna didn't interest him, but in the Future, Tsuna has already gained his respect. Hibari states the only two people that make him happy to fight are Reborn and Future Tsuna. Together with Irie and Vongola Decimo (Future Tsuna), they planned to send Tsuna and the other Guardians from the Past to the Future. He was the only Guardian Tsuna informed about this risky plan. Tsuna also sees him as a valuable comrade and thinks very highly of him. More often, though, Tsuna sees him as a scary person and doesn't want to incur his wrath. In the Inheritance Ceremony Arc, when Tsuna lost his will to fight and got depressed, Hibari confronted him and said: "Little animal, your face is boring. Watch my fight closely." This may have been Hibari's way of encouraging Tsuna, and could also mean that Hibari has started to acknowledge the current Tsuna's power. He declared to Adelheid that "he will one day bite the sky", showing that he has a desire to fight Tsuna. He sometimes addresses Tsuna as "small/little animal". Considering that he likes small animals and their determination, this may be his way of showing that he doesn't hate Tsuna and acknowledges the latter's willpower.
The greatest sign of Hibari acknowledging Tsuna, potentially even respecting him, is when during the Curse of the Rainbow arc, Hibari was fighting against Dino after the second day of the representative battle, and Tsuna told that that he had something to tell them. The moment that Tsuna showed how serious he was, Hibari stopped his fight with Dino to listen to him, a feat that is very rare, especially as Hibari was very determined to bite Dino to death. In the future, when Tsuna stopped a fight between him and Mukuro, Hibari didn't mind and even asked Tsuna to spar with him in Mukuro's place, though Tsuna declined.
Both of them are the two oldest Guardians. Ryohei acknowledges Hibari's power and had already visited his house several times to challenge him but was always beaten by him (according to the art book). On the other hand, Hibari only sees him as a "noisy animal" and treats him like the others. However, in the Future, they seem to already have some mutual respect. Ryohei even suggested they drink together at some event but Hibari refused. Sometimes their thoughts clash and create arguments about minor things, which ends up with Ryohei challenging him to fight. In the Primo Family Arc (anime only), Ryohei is the only one who manages to convince Hibari to take the trial. This makes Ryohei the second person to be able to convince Hibari on something, after Dino. Ryohei is also the only person who makes an effort to befriend him, much to the shock of others. Ryohei's efforts have not been in vain, and their future selves seem to have a much better relationship.
Dino is Hibari's home-tutor during the Ring Battles with the Varia; however, Hibari doesn't see him as his teacher and doesn't care about it, only wanting to bite him to death. Dino sees him as his student and acknowledges his skills when he trains him, but also finds it hard to train him since Hibari has no interest in listening to him. Moreover, Dino seems to be the only one who can convince Hibari to stop fighting, though at first, it was very hard to do so. However in the future, he is able to convince him more easily and always accompanies him if he "runs off" because of his dislike of crowds. Dino thinks of him as a reliable Guardian for Tsuna. Hibari doesn't seem to hate him, although is sometimes irritated by him. Once in a while, Hibari will take what Dino says into account.
Hibari tells Dino that one of the reasons he joined Team Fon was to bite him to death. Upon Fon asking the reason why, Hibari reveals that Dino was the first person to ever want to be his mentor, stating that he has no need for such a thing, and so he wants to win against Dino to prove that he doesn't need him.
Hibari and Fon are related to each other, though the details of their connection have yet to be revealed. Hibari represented Fon in the Arcobaleno battles and the two were shown to be comfortable with each other. Fon was reluctant to let Hibari fight the Varia by himself. Hibari physically resembles Fon, though their personalities are rather different.