Here's a little extra note about why i think their relationship is toxic coded :
Yeesung is someone with a lot of trauma who has built up a strong persona to hide behind. When he meets Gyeol, he lashes out at him, and Gyeol responds with his own strength. The beginning of their relationship is like a literal fight until Yeesung realizes that Gyeol is strong enough to carry some of his burden. From there, he lets his vulnerable side showand grows to have honest feelings for Gyeol, perhaps for the first time. I think he also feels reassured by seeing Gyeol's brute side because it's proof to him that Gyeol can protect him, even if he gets tossed around a bit in the process. Gyeol is like a tiger, working on primal instincts. He bites, protects, and loves, all in a flawed way, but that's okay for Yeesung. Because he see himself like someone broken, afraid to never be loved for who he's inside.
I think their relationship can work if Gyeol work on his shitty temper and Yeesung learn to stand for himself.
I got back to the first chapters to try to make sense of the story again, because the later chapters were really confusing, and i noticed few things along the way. Sharing it with you ~
Spoilers
Gyeol was a target from the very beginning.
When Yesung noticed him, he probably told his boss about it. After that, Gyeol found Yeesung getting picked on in an alley, which was strange already for someone that strong... unless it was an act by someone knowing Gyeol's tendency to pick fights. (there is several police reports about this probably easy to get the hands on. )
After that incident, a man is seen standing outside Gyeol's house. Contrary to how it looks, it's not Yeesung (his shoes don't match) 'probably his boss.
From there, there are two possibilities.
One is that Yeesung's boss told him to befriend Gyeol, to hire him for fights later. One clue pointing to this possibility is Yeesung's strange behavior ( the fact that he was not that friendly and was even more predatory than ever during their first encounter ). Not replying to texts and all like it was more a burden than anything.
Another possibility is that Yeesung is doing this for fun, like a cat playing with its prey. Yeesung's ego is huge, and he looks like the type to easily use others for fun. (Or, he could be manipulated into thinking he's doing this of his own volition.) In that case, he was not instructed to recruit Gyeol, which is why he tried to dissuade him to join the fight.
In both ways, Gyeol also weirdly lose his job. Making him more likely to sign in the tournement for the big prize.