In the Zoldyck family their was a boy who was known and well-recognized in the assassin's world for his talent in assassination. His name was Yilluzu Zoldyck, he was the eldest son in the Zoldyck family but even with talent and potential like that he was never titled as their heir.

Why?

Yilluzu was perfect in every way but there was one problem, he has a weak constitution, often got sick and has a fragile body. That's why his parents won't allow him to be the heir and give him the responsibilities that was tied within the title.

The Zoldyck family love him very much that even just a scratch on him would be a big deal to them. Yeah, I know right, he is an assassin but was treated very delicately and with fragility.

But midst the family being overprotective to him he still got injured from his last mission back when he was 12 years old.

You ask why would the family still give him mission when just even just a scratch on him will make a big deal to them? Well, Yilluzu like his family's profession. He loves killing and assassinating, that is why he can still get missions by persuading his parents to allow him.

His injury back then was very severe, his life was at stake so his parents sent him to their private island to recuperate with the help of all the family doctors.

Yilluzu was in coma for the whole 13 years. His father and mother just frequently visits him and hopes that their beloved eldest would someday wake up.

They will tell him stories about their missions, how they are doing and how they really wanted to see him open his eyes again.

Unbeknownst to them, even in coma Yilluzu could still hear them but was unable to control his body to wake up and move.