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Basically if the remaining part of the demon is in him or not iirc. The novel translation I read got really crappy at this part but it’s related to the demon who hid a part of itself close to Seungjoo. I think he either lied and brushed off his original question (because gwangsik is clearly having his own struggles and doesn’t need more piled on him atm) or could sense the answer and no longer needed to ask (I forgot which it was but that was the question).

What was the questuon Seungjoo was going to ask the blond guy but already got the answer?