Muzan achieve his dream to be a perfect being.. He have conquered the sun and live as a immortal being.. As the time goes on, he no longer turn anyone into a demon anymore.

He poses as a wealthy man in modern time, still conducting experiments out of curiosity.. And that led him to have a rock size mini version of himself.

One night, on his way home, he realised that he lost his mini self.. He spent hours searching for it.. That thing contain his blood and can turn people into a demon with just a small bite to inject his blood to another.

He saw you holding his mini self near an alleyway.. He keep a safe distance.. He just silently watch as you get up and start to walk away with his mini self.. He need to get that thing back..