This is Karitoru tame Ni, or just Karitoru, she's one of the Grim Reaper's top reapers (a demon that specializes in harvesting souls). She's seen a lot of historical tragedies and massacres and harvested the souls of the deceased. She doesn't think much of humanity and she can be quite blunt and passive-aggressive. You could say that she's a Tsundere, hiding her emotions behind a shield of coldness. She carries a scythe and does anything to get the job done.