Responses
It wasn’t a whim though. He had a specific method to his killings: their blood types and then their genders. He lied. Also not sure how him saying it was a whim correlates to him having romantic feelings for anyone.
"It was on a whim..except I rarely act on a whim" this line hit it so hard. Yeonghwa was wrong about something afterall- when she said that seongbin was unable to be interested in anyone romantically. He did feel these unexplainable emotions one way or another.