I'm thinking about the title...

In Greek mythology, Sisyphus was a human who created the ancient city Corinthe, much like Guwon created his own haven in the middle of literal hell, but is more commonly known to have cheated death twice, defying the Gods. He was condemned to endlessly roll a boulder uphill, only for it to roll back down each time he reached the top. This endless, futile task is the origin of the term "Sisyphean," which describes a task that is extremely difficult and ultimately pointless. I believe Guwon is either the reincarnation/embodiment of Sisyphus in this stories reality or even metaphorically, and his endless task is in attempting to regain his humanity as he is no longer really human nor does he seem to understand basic concepts like emotions. I do think he's undead in some capacity, maybe having those scars from severing his limbs in order to remove bites to prevent becoming mindless, or was the product of experimentation and Guwon could be the product of someone else, hence it being called "The Hounds of Sisyphus". He could have been made this way and is incurring some level of Sisyphean punishment much against his will... I have a feeling the vomiting after kissing is a red herring and has to do with his body rejecting the humanity he possesses while being undead... TLDR, this is gonna hurt, and I don't think Guwon is manipulative but grappling with an endless cycle of punishment.