First. I don’t think she can do it again.
It started with Soul Taker, his real name is Kek. So Kek can’t control his demon powers but his younger brother can, he’s perfectly fin controlling himself, Kek as a half demon and half grim reaper dangerous mix. When Kek started working as reaper he followed the rules but slowly losing control of himself started killing randomly people, he soon discovered his demon powers started using shadow abilities to kill his victims, he prefer using shadow ability to kill his victims in very painful away ( pulling victims apart is his favourite way to kill his victims) that’s when he had nickname Reaper Without Mercy, he dosen’t show any mercy to anyone, will kill anyone in sight. Kek started killing other reapers which a huge crime. The leader of grim reapers order his mother to take her own son’s life, she couldn’t do it when Kek lost completely control he almost killed his brother but his mother stopped ( I was thinking that the scar that One Eyed Kid was from his older brother’s scythe? ) his mother use magic to locked his demon powers into necklace making him forget about that’s part demon, father and the event.