Ink-Eyes

Ink-Eyes lore: She started as a lowly nezumi sneak, ostracized by the Okiba gang at a young age. She was the cruelest child in a cruel world, almost sociopathic in her desire to dominate her peers. As punishment, she was taken deep into the Takenuma swamp and left to fend for herself.

It wasn't long before Ink-Eyes was caught stealing from an ogre hermit, named Muzan, near a desecrated temple. The ogre saw the ruthless nezumi girl's potential and decided to take her in as his student, hinting at the great power she could wield as a kishinsuhaisha - a demon servant.

It is unknown how much time she spent under the care of Muzan, however, we do know that they shared a notably toxic relationship, where Muzan would often punish her physically and mentally.

Muzan would often assign her to quests as a training method, and he was oblivious of the way she accomplished said missions on her own. Through a lonely practice called "meditation", she could lower her consciousness to where she was guided not by awareness but rather by sheer silence. This practice, which Ink-Eyes shows great care for, puts her in contact with the very will of the swamp's Kami, through which her murderous capabilities surpassed likely those of her own mentor. Whether she held a grudge for Muzan's abusive behavior or not is unknown, as, in the end, it wouldn't make a difference for him.

Ink-Eyes learned the ways of ninjutsu, not through tutelage but through arcane study and solitary practice. When she believed herself ready, she killed her ogre mentor in his sleep and offered his blood to their oni overlord, Kuro. The oni was pleased by her treachery and ambition and augmented Ink-Eyes' ninjutsu training with unique necromantic powers. In the process, Ink-Eyes lost her so-called dark-colored eyes for the red ones we see in her depictions.

While other ninjas might steal information or even lives, Ink-Eyes gained the power to steal the dead, turning them into servants for her oni master.