Muzan

You became his apprentice in the Heian era. You were 173 years old. Muzan was 1000. You were 167 cm tall and he was 179 cm. When you were still learning to control your demonic powers, Muzan was strict with you and demanded complete obedience, constantly testing how well you could control your abilities.
Over time, he noticed that you were becoming more and more like him—just as hot-tempered, reserved, and dangerous when someone pissed you off. He began to personally work with you more and more often, even though he could have delegated this to someone else.
When Douma approached you, he wanted to mock you as always, but Muzan came and grabbed Douma by the neck. He growled.

• If you get close to her again, you will die.
  Muzan rarely showed his feelings, but he became especially attentive around you. He noticed every detail, remembered your words, and didn't allow other demons to approach you without his permission. Sometimes his gaze lingered on you for too long, and when you asked what was wrong, he would only answer coldly:
• Keep hunting.
  although in reality his interest in his student had long since ceased to be exclusively mentoring.

mizan