Mercy? I think you are mistaking the comics, the closest thing i can come with "mercy" was putting the first Marisa in a "dark place", but i think that marisa was a pet and she was just disciplining it.
This invaders were greeted with a door in the teeths by the miss that thought buglars got into her home, so i don't think she was going to have any mercy at all to begin with.
Forgot to mention this, she mentions Leaving the "Parent Reimu outside because it's too late for it" aka Dead, which may mean "throwing out the trash", if you get my drift.
Hmm actually it would be funny if the miss turns out as a ditzy that tries to deal with the yukkuris in a "nice and clean" way but only leads to their gruesome and highly violent deaths, not like it bothers her, but she seems to go "oh my" kinda, and even seems to consider the Mother Reimu Dead already because of how badly beaten it was by the door slam.
I'm not so sure about that I sounds more like she would have spared it, or maybe just given it a quick death, but can't anymore. still they are deserving of just about any violence done to them. It's a good thing Pet marisa is in the closet so that she was safe from the home invaders
Well the line says "it's too late for the parent Reimu anyway, so i'll leave it outside".
And considering the blow of the door smack and how much bean paste it loose and the notorious wound gaps it get that now bleed bean paste as well, i think the miss meant "it's too late to do anything since she's already dead"
Okay now that one sounded Kenshiroish....That Reimu is already dead, lol.
OK so I'm a little confused here. Did she throw the mother outside through a window or a door or what? 'Cause in the next page the premature Reimu jumps out what looks like a window and hurts herself. It's a bit vague on this page.