Royal Servant has not been clearly a black or white story though, so I think to judge Christoph as a character who deserves to be punished for only his actions is unfair. If characters who have done evil deserve to be punished, the same could be said for Lucaon and Kyon.
Lucaon raped and used Kyon as a sex outlet at the beginning of the story. Lucaon also threatened Karis and almost hurt the poor servant, without any consideration of how hurt Sihan would be if Karis were injured. Readers seem to ignore Lucaon's past actions, because of how much Lucaon loves Kyon by taking care of the youngster and finally engaging in consensual sex. Lucaon said he would treat Kyon well, but he never said the word "sorry" for all the terrible things he has done LOL. Kyon's emotional confusion while he was with Lucaon should never happen to anyone. And I don't think being traumatized excuses people for disrespecting others either.
Kyon almost killed Lucaon when the Selvior family's mansion was attacked. Yet, readers don't seem angry at Kyon because Kyon did not have his own autonomy at the time. What's different about Kyon and Christoph is that the former lost his memories, so he behaved and was confused, while the latter kept his memories, but it doesn't change the fact that he lacks autonomy... :/
Readers could clearly hate Ryan for telling Kyon to leave Lucaon and when Ryan was even happy when Kyon cut his own neck, but now the attention is shifted to Christoph, so some people may have moved on from that. Maybe readers forgive Ryan because he apologized to Kyon and won't hurt our poor servant anymore.
I think a character could be hateful if they had the ill will and actions combined. I don't know if Lucaon knew what he himself desired when he mistreated Kyon, but we learned overtime that he is caring and loving but needed time to open himself to others again after his family trauma. We know Kyon would never willingly choose to hurt Lucaon and would rather kill himself instead. And Ryan just wants to protect the Selvior family, so he chose Lucaon over Kyon. I don't see why people are hating Christoph, who once again, lacks autonomy and was living life the only way he knows it (following Edwin's orders). I think people could argue that Christoph could have changed after being a servant by not listening to Edwin's orders anymore, but that's easier said than done; Christoph doesn't even know what it means to have his own autonomy, and he was just beginning to learn that through Ryan.
Is this difficult for some readers to see? Kyon and Lucaon have each other, so at least they can comfort each other. But poor Christoph is alone... :// Even though Christoph lives with Karis and Sihan, Christoph can't tell them he's part of Intron, or that he's conflicted because he cares for Ryan, but he feels obligated to follow Edwin's orders. It's a lonely life to live when you can't share your concerns with anyone. ┗( T﹏T )┛So, why not hate Edwin for contributing to Christoph’s tragedy, as well as Kyon’s and Lucaon’s tragedies?

Our focus is on Christoph. I don't see the story with a black or white lens. I acknowledge it was wrong of Christoph to poison Lucaon and cause our main couple to suffer. Yet, I see that everyone is a victim in their own way. There's a web of suffering for the characters. Besides Lucaon who lost his parents and was traumatized, and almost lost Kyon, and Kyon who made those painful attempts to leave Lucaon, Christoph suffered in his own way before he became a servant for the aristocrats. ://
We could see that Edwin didn't even care for Christoph when the older brother asked, "Why do your wounds take so long to heal?" We saw Christoph get mistreated last chapter, and Cecilia even said this chapter, "Some families are a bit sensitive about illegitimate children and cast them out." We know Christoph is part of Intron and is in contact with Edwin, so we can't say for sure if Christoph was kicked out of his family or not, but he clearly wasn't treated with love and respect. I'm not saying Christoph's actions are forgivable, but I certainly feel sad to know Christoph is just so AFRAID.
Christoph is a young adult who flinched at the slightest human contact. :(( Christoph couldn't trust or form loving bonds with anyone. Christoph is just used as a tool to fulfill Intron's missions/listen to Edwin's orders, which is like Kyon. I'm grateful Kyon has Lucaon by his side, but what about Christoph? Christoph must be so touched by Ryan's care and gentleness; I bet Ryan was the first person to tell Christoph, "It is my job to protect you," which demonstrates that Christoph is valuable and cared for, and a pat on the head from Ryan wasn't threatening, but tender... Ryan even acknowledged Christoph, "You're so nice," unlike Edwin who would just order Christoph around like a robot. ://
I'm not certain whether Christoph has romantic feelings for Ryan or not... But I can say that it seems Ryan has shown Christoph that our young mixed-blood isn't simply a tool. Based on what we've seen so far, it seems Christoph has just lived his life being mistreated and obediently followed Edwin's orders, without being ALLOWED to have his own autonomy and consider his own desires. ://
There is still more we could learn about Christoph. I certainly think Christoph isn't intended to be a character who is supposed to be 100% evil, otherwise the authors would not need to write his backstory and get -at least some of us- sympathetic. ┑( ̄Д  ̄)┍
Maybe it would have been better if Christoph's memories were erased like Kyon's memories... Maybe Christoph could have embraced the new people around him and form meaningful bonds. But sadly, Christoph was conflicted: the poor boy knew and was told to follow orders, but he didn't know what to do when Ryan was so kind to him... If Christoph's plan was simply "...to approach [Ryan], and earn his trust. ...find out what he's up to, and report it to [Edwin]," maybe the story wouldn't have been as complicated as it is now. Unless Christoph was ordered by Edwin to poison Lucaon, does that mean Christoph chose to poison Lucaon on his own? And what for? To protect Ryan because Christoph knows Ryan would protect Lucaon? Maybe getting rid of Lucaon would mean that Ryan would have less duties on his shoulders and likelier to be safe??
When Edwin noticed, "You seem a bit...different, somehow," and Christoph shared that Ryan "seems like a nice person," there was a change on Christoph's part. Christoph was no longer the robot Edwin knew; Christoph developed his own opinions on a person and was no longer afraid of physical contact like he used to be. When emotions are involved, the mastermind loses the complete control they used to have over their minions.
Not related to Christoph at all, I do like that we know Cecilia is the head of the Dominus family. It's refreshing to not see a patriarchal family. Even the Selvior family had Lucaon's mom sit at the head of the dining table. :))