Responses
Agree. Like any poison in small doses over time can kill you slowly and remain undetected. I also think that Christoph knew he was about to be outed so he killed the only one who knew the truth. I think he's got a grudge against Ryan as well possibly for giving him away and going to sleep
Maybe he's killing Ryan as well. I mean he is afraid of him, just another thought
I think it is Kyon's body that is the problem, since everyone, including Edward from Intron, know that Kyon is not strong enough to actually hurt his master. Therefore I think they added the VS solution into his blood or something, so each time Lucian sucked Kyon's energy, he took some of the VS solution..
Or it could just be the person, who broke into Sihan's house added it into the tea or something, before he died..