These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Yuki: Stockholm Syndrome victim and helpless uke that constantly needs to be saved from holding the Idiot Ball, or a believably traumatized victim who tries to take the option that involves being there for Jun and not killing, to his own detriment?
Ashiei is a member of the Yakuza, like many characters in this manga, but what distinguishes him is the fact that he raped his stepson Yuki and sold him into being a sex slave when Yuki was only 12. Years later, he shows up again, stalking his stepson. When a friend of Yuki's tracks him down to confront him, Ashiei brags about his stepson's "talents" as a slave and about raping him. He reveals that he's stalking Yuki out of revenge for being left with burns from a fire that Yuki set to escape him, because his looks were ruined and he's in pain, despite the fact that Yuki showed mercy by not killing him. When he finds out Yuki is still alive during their confrontation, he gloats about how he wants to rape him again, and tries to do so until Yuki escapes. He was a Stalker with a Crush on Yuki's mother, took the opportunity when her husband died, possibly raped her as well, and was a factor in her suicide. He's unable to work with pretty much any gang other than Wang's triad, because of his behavior that ranges from unstable at best to purely sociopathic. Even the other Yakuza reject him.
Wang shows up upon the scene of Ashiei and Yuki fighting years later. He reveals himself to be a False Friend of Ashiei's, offers Yuki a loaded gun to finish him off, then, when Yuki hesitates, shoots Ashiei himself. However, it turns out he was the slaveholder/pimp that bought Yuki from Ashiei. He is an owner/seller of child prostitutes. He didnít help his former victim out of any noble cause, but instead wants Yuki, now seventeen-years-old, for himself as his personal "pet," as well as using him as The Mole against an opposing mob boss that's actually treating Yuki with some degree of respect and caring. By kidnapping Yuki and holding him hostage, along with his previous actions to consolidate power, he's also managed to turn the heat up on a Mob War that had grown somewhat cold after the first round of deaths.
For Ashiei: Raping his stepson, then selling him into sex slavery at 12
For Wang: Being one of Yuki's "customers" (a.k.a. a pedophile and rapist) and finding him again at 17, pretending to rescue him from Ashiei, giving him a Sadistic Choice that he fails badly, then kidnapping him as his personal "pet" once more...
Rape and sex slavery are common parts of the "criminal underground," that leave a path of trauma and suffering through the lives of those affected.
Love and respect for others gives one true happiness, not power.
Seeking power at any cost just leaves everyone dead.
The Farmer and the Viper: When dealing with some people (specifically those who make a life of exploiting others and yourself), offering kindness or mercy can be the worst mistake possible, as they will see it as a weakness.