Unmarked spoilers are ahead, per Spoilers Off rule.
The entirety of Ash and Eiji's relationship. It's a bond so important and precious to both teens it's hard not to wish for them to be able to stay together forever somehow.
From the get-go, Ash has had a soft spot for Eiji. When Eiji naively asked to see Ash's gun and about his life as a gang leader, Ash hands it to him and answers his questions. What's astonishing in that is that apparently, up to that point, anyone that has tried to even touch Ash's gun has been shot in retaliation and yet, he let's this awkward and innocent teen take it and in no moment does he shows any sort of ill-will towards him.
Also, Ash giving up his gun when Eiji is threatened by Arthur. He met the kid literally a couple of hours ago, exchanged a few words with him and yet, is obvious Ash would put himself at risk for both him and Skipper.
Eiji's pole vaulting and what it represents. While the height was nothing compared to previous times, there were also none of the security elements that would normally prevent an athlete from suffering a grave injury if something went wrong nor are the circumstances the most ideal, with dangerous criminals closing in on them. But Eiji still wishes to put himself in danger to somehow help Ash and Skipper who have done nothing but try to keep him safe and unharmed at their own risk. This also marks the first time that Ash realises that Eiji is fundamentally different from others, in that he expects nothing in return and seems to genuinely care for those around him.
Skipper's bond with Ash is also an important part of the latter's life. Skip was not only an assistant of sorts to Ash, keeping him on the loop about what was happening in the streets and with the police, but also a close and dear friend, to the point that he was the only one that knew about Griffin and his connection to Ash.
How quickly Skip and Eiji get attached to one another. The former was impressed with the latter's courage when asking to see Ash's gun and declares that he likes him. When the bar is attacked and after they're kidnapped, Skipper does what he can to protect Eiji, even though he's the younger one in the duo. Eiji, while terrified and completely out of his depth, clearly tries to stay close to Skip and find a way to get help.
Shorter's friendship with both Ash and Eiji.
He met the former in juvie when younger and has been a close ally and confidante for years. He recognises the pain that Ash has suffered in his life and has grown to be protective of him. He's the one that raises the alarm to Ash regarding the betrayal of Arthur and even leads a rescue operation to retrieve Ash and Skip.
With the latter, even though he has barely spent time with him, he has gone above and beyond in keeping him safe. He keeps a close eye on Eiji and easily becomes a close friend to him. Whenever there is danger and Ash is unable to help quickly, Shorter is the one that pushes Eiji out of harm's way.
Ibe and Eiji's friendship. The reason Ibe got into photography was because he saw Eiji pole vaulting and felt inspired by him. When Eiji had his Career-Ending Injury and felt depressed, Ibe was one of the most worried and decided to take him with him to New York City to give Eiji a chance to focus on something else and see more of the world.
On the flip side, we also have Max and Ash's bond. At the beginning, Max was asked to help protect Ash in prison as a favor to Charlie and Ibe but, when they found out the connection they had through Griffin, their relationship strained temporarily, with Ash blaming Max for not doing enough at the time. Nevertheless, once they got past that, they became close allies and friends to the point that Max sees Ash as a second son and Ash trusted in him to understand what and why he was doing what he was doing.
