Despite Endeavor's temper tantrums, Hawks never seems to be scared of him. Endeavor calls him a "little brat", which implies he still thinks of Hawks as very young. Hawks is revealed to be a huge fan of Endeavor ever since he was a kid.
The two get along well, despite Endeavor's brusque attitude and Hawks' constant banter. Hawks even requested a team-up with Endeavor as he needed his help in investigating concerning sightings of Nomu.
Endeavor and Hawks fought together until death against Hood and won only due to a combo attack. Endeavor is easily provoked by Hawks but also shows slight affection to him. He even appears solicitous when he tells Hawks he should ask for help and not expose himself to any greater danger.
Hawks felt guilty because of the scar that Endeavor received on his face, although he could hide his sorrow. Endeavor knows Hawks' attitude and facial expressions very well, even to the point where he was able to decipher Hawks nonverbal warning.
It's revealed at some point during his childhood, Hawks was saved by Endeavor, which caused him to greatly admire the flame hero and desire to shine as brightly as he does, even buying a plushie of his idol.
They appear familiar with each other, as Hawks visited him after the Kamino Incident. It is implied Hawks was responsible for Tsunagu's disappearance.
Dabi is the first one Hawks has contacted in the League of Villains and the first person, to make Hawks change his nonchalant behavior for a moment. After the incident with Hood, Dabi was confronted by Hawks asking why he broke their promise on the Nomu that was supposed to show up. While doing this, Hawks threatened Dabi by holding one of his feathers close to his face. Hawks was disgusted at having to deal with Dabi as seen when he walked alone, but towards Dabi he keeps a friendly and serene facade.
Hawks knows Dabi wants to use him and is aware of Dabi's distrust. He allows Dabi to take advantage of him and plays the fool in order to let Dabi forget about the risks and to steer Dabi's focus on the returns. When Hawks offers Best Jeanist, he gains a more of Dabi's trust. Not because Dabi completely believes in the credibility of the corpse, but because he sees Hawks being able to commit a murder. Dabi is counting on Hawks' "dark side", the hidden part of his personality able to kill in favor of his goals.
As Hawks enters the inner circle of the Paranormal Liberation Front, Dabi states to Hawks that he "looks happy". He subliminally states that he is still observing the hero. Dabi enters Hawks personal space, which implies Dabi’s gesture is simply a display of dominance. Their relationship is based on mutual exploitation.
Once Hawks revealed himself as a mole, Dabi wasted no time in assaulting him with his Quirk and stomping on his face. In the fight against him, Dabi calls out Hawks' real name, which had been kept secret since Hawks was a child. After Hawks killed Twice, Dabi forces Hawks to the ground and burns off the last of his wings. Hawks asks who the villain really is and Dabi answers his question. After hearing Dabi's real identity Hawks stops struggling and goes into a state of shock. Dabi tells him that Hawks should have known, Dabi was a bigger threat to him than any other villain. Dabi then claims that he does not care if Hawks lives or dies, but before he can do his next move, he gets interrupted by Tokoyami.
Hawks would put up the façade of being a loyal soldier by reporting about Endeavor's activities.  He also pretends to be fanatic by reading one of Destro's liberation books and passing them out to heroes, something Re-Destro thanked him for. However, it is revealed Hawks was sending his fellow heroes messages about Re-Destro's organization.
The relationship between Hawks and Twice grew very close and complex. Hawks helps Twice to understand more complex themes about Destro's ideology, supports him, and gives him friendly tips as to how to speak to his soldiers. Hawks claims to have feelings of being trapped in the hero system, without really belonging anywhere in order to gain Twice's trust
Hawks recognizes Twice as a kind-hearted person despite being a villain and developes a friendship of sorts with him. Twice wishes he could "get rid of these bugs" on Hawks' wings and shows multiple times how much he trusts the winged hero. He states that Hawks "can't be a bad guy" and wants to free him from the hero society. Hawks shows multiple times that he doesn't enjoy using Twice to gain information, however, as he's usually seen smiling sadly at Twice when the man's back is turned.
Once Hawks confronts Twice, he explains his motives and asks him not to resist so that the police can detain him. Even after showing his true allegiance, he claims to understand Twice's tough situation and offers help Twice get back on his feet after paying his dues, and openly stating that he is a good person, but calls him "unlucky." As Twice refuses his offer and prepares to fight back, Hawks tells him to stop, saying that he doesn't want to fight the villain however Twice responds to this by saying that sounds like a "you problem." and prepares to summon more clones to fight. 
Even after easily defeating Twice's clones, Hawks tells Twice that if neither hero nor villain will give up, one of them has to die. Despite this, Hawks purposely makes sure Twice's injuries were non-fatal so he could bring him in alive. However due to continued resistence from Twice and Dabi's interference, Hawks ended up killing Twice by stabbing him in the back as Twice flees to join the battle in order to stop him. 
Hawks admitted he took in Fumikage mostly because he wanted information about the League of Villains. The first time they had met, Fumikage could not keep up with Hawks. The heroes that worked with him told Fumikage that Hawks was just too fast and they would usually deal with the aftermaths of Hawks' fights. But Fumikage gained Hawks favor due to the amount of potential he had.
After the work studies, Hawks once again asked for Fumikage during the Shie Hassaikai Arc as they trained together. It's shown that Hawks is surprised at how Fumikage keeps up with him during patrolling. After the patrol, Hawks takes Tokoyami on a flight to show him how much potential he's wasting. With the help of Hawks, Fumikage devises a new move named Black Fallen Angel.
Hawks likes to joke about them both being birds and stated he is happy Fumikage being the one who came.