I do believe it was Miss Nanaly. In that world, I think she had some ability to explode hearts, or the like. There was a guard who was holding her who died in that way, and the pain in my chest was...well. Quite a blast.

[....]

[He just. Looks away.]

I would've killed Miss Susato if I hadn't been stopped. I had already killed Mr. Joonghyuk, and Miss Nanaly died not long afterwards, because I had shot her. [......] So that is why I am grateful.