I look at it kinda like an inccubus. I think the "toxin" is the aura that mc give off. You start to develop this and sense of desire for him the longer you are in his presence. He's very alluring. I think it kicked in for the king after the mc was pushing the porttait thing, also mc isnt really scared of him so it might of made him curious like "who the hell does he think he is?" I think that's how the poison works. It makes you curious in a way, if you read past 20 it kinda happend again with another character (wont spoil it) after that grew, i think him smiling was kinda like him being cheeky in a way, and over time it just builded up as infatuation. That's when the Kings infatuation burts out (hate curiosity digust allure etc) and got to a point were he was so enthralled in his thoughts of him, his intrusiveness took over. The more you are around their kind, the more you get enthralled into their aura, their essence. Their poison. To the point you go mad. That's what that's how I look at it.
So here's my take.
The Imaes' bodily fluids are poisonous to anyone else but other Imaes. However, I believe that due to the MC being half-human, unnamed, and beautiful that his particular use of "fire," is that of burning (or obsession). He cannot consciously use fire as an element like other Imaes because he did not go through the Naming ceremony, and never will. When the ceremony takes place, an Image is given a name and blessed with fire from the village leader. But, again, this doesn't mean fire can't form in other aspects just because you don't have the leader's particular type.
No-name's "fire" can be seen "spread" to a few characters who end up endlessly pursuing him: the Chieftain's son, Garon - The Emperor/King, and this guy. They are obsessed with him, they want to own him, they want to spoil him, they want to keep him, and sometimes all it takes is to be around him in order for the "fire" to start spreading.
With that said, the MC broke one of Garon's fingers and Garon acted like that shit was a wedding proposal because he just broke two of the MC's fingers. ┑(￣Д ￣)┍
no damn this makes sense bruh all the men here are insane (ʘᴗʘ)
i dont get ch 23 can someone please breakdown why MC and the king suddenly changed their atmosphere like 1st half is them fighting and then the next king is kissing the tears away. like bruh