The female leader is also the halfsister of the princess but they don't know it yet.

It's been a while That Nox was Seen After He had become the demon King.
He got To he** To ether whipe Out the Rest of demons That where still loyal To the old demon King and the Rest followed him-
But Just the strong one.

After years Nox the Traitor came back.
And the Rest ist Like in chapter "0" That you can read there.

It's hurt.
It's sad.
He had To kill His own father for the demon King To die.
The one to die should have been Nox.
He wanted His father To Life on-
To be happy.

Nox He got mad.
He could feel it.
But Nox did Not defekt it.
He is dead.
He have His all to save them all but they told Theo-
They told His father about all and now He had To kill him To kill the demon King.
Now He feelt hate.

Hurting
Sadness
Hate
Madness

It's them,
They killed My father.
He's crying Like never before.
He's own willing To Protect turned into new hurtfull memorys.
This Moment wich should Be the Happy endind for all turned into sadness Just for him.
His Love for them who Had His father come over turned into Hate.
And That all became His Madness wich turned him into a even stronger demon King AS the Former one.

Nox the demon King and Traitor To humans was Born.

Nox was shocked.
With the Demon King inside Nox father Theodore He told Nox about how He found out about it and why He is there.
Theo did know, He had sinned against His joungest son Nox who did Not Had Care in His Family.
Even less after the "death" of Nox Mother.

Even so Nox did grow, He opened His Heart To this world and it's people and stond Up over and over again-
All without him.

He wasn't a father To him but He is proud of Nox and thats is why He is thankfull To Nox Mother even knowing, That she came only in His Life To give birth to Nox Just To Take her death later on.

Theo Loves His son Nox and now it's time.
Before the Demon King is able To control Theos Body Nox has To k*ll him.

So He did.
With tears in His eyers He Said To His father before His Last taken breath, That He could never really hate His father, calling him the First time after His mothers "dea*h" father.

I don't know how anymore but Nox fount the demon Kings Spirit offering him His Body.
The demon King Happy about a Body this good was Just about To Claim Nox Body as Nox father came.

Nox, wondering how and why He is there got loud screaming at him That He should Go.
I don't know what and how it went anymore but the demon King got into the Body of Nox father instand of in His own Body.

It was already To late.
Nox father Had Heard about Nox past lifes, His wife (Nox Mother the Engel and g*d who Had odered her To give birth to Nox) and Nox plan To sacrifice His own life (with only a few days left) for all the Others-
Even His own father despite their broken Relationship.

Nox Said That He was the only one who could Take the role of the sacrifice but they-
Nox, His Master and His father After Hearing all of Nox from His Master and His Dragon teacher He decidet To be a father To Nox by Take His role over.
Nox did know after all That His father would make a good sacrifice but never acknowledged To sacrifice him.
Nox never even Said That it would do it bit they found out about IT and more surprising, His own father came there for Nox.

After the war with the demons startet, Nox was busy protecting and so on.
To Protect He have Up more on His hamanity wath was To See in how His own Body could transform Like demons.
Even by fighting for the Humans on the Front they soon feared Nox and began To doubt him, who Just Protected them.

The human Armee soon did Not See him as and Ally anymore and even so, Nox did Not hated the Humans even playing the villain for His friend That never doubt es him- 
So That His friend would to be attacked by people After He is gone.
This day is His time to confront the demons King.

Demons-

Once Humans That betrayed the goddes after they Had Stolen a Part of her she once left behind for the Humans Future.
They wanted more- 
The Goddes herself.
A war beetwen the demons and the Angels broke Out.
Tree demons wanted betrayed the demon King and they became the First heads of the so called DARK Familys.
Demonkin lost and where banned from the world into the he**.

The demon king Deos Not have a Body on His own, craving for a Body of the reinhafer dark Family with much of dark Energy so He can escape he**.
Nox want To offer His time Limited body To the demon King Spirit To Take over, use the time the demons King needs To get Nox Body unter controll (ca. 1 min) and be killed by His master with the Swort moon Art before the demon King can controll Nox Body.
After all only If the demons King has settled in a Body He can be deafeted.

Alfter His people and his Master Heard Nox explain all of himself and His plan To defeat the demons King they were shocked, sad and weak knowing That Nox would never Stop and after all That He went througt He would give His Life happly To Protect them forfeiting his own future.

Now they want To save him

So His mother Put His Soul To another world and He played the Game as Yoo Chan.

Found it.
Thank you.

In the end of the Novel Like in this chapter "0" Nox Said the Same words to the "Original MC" in the Same Situation.
He had become the new demon King and for real I can only feel with Nox.
Why?

In the Novel with Nox as the MC, he really did His all to Protect.
Always and in every time.
After He meets His mother who wasn't actually dead His mother told him the treu about His birth.
G** had given an Angel (His mother) the Mission to given birth to a child with the Family head of the reinhafer.
This one is Nox.
Also the Game wasn't Just a Game Yoo Chan played but all His past.

Nox was merly Born ro be a weapon against the demons with the curse of Limited Time Cast by His own mother in him.
Everytime he failed he got To the past without His memorys.
He only can end His loops If No demons are left.
His memorys Always came back later in pieces but too late.
Even so Nox never hated His mother or any another human for it and hoped To save all in His next life.
He himself gave never Up to save Others and the world so He was willing To Go Back in time over and over again.
He Always did His all to Projekt His Loved one but failed 26 Times.

that the princess drugged him for it in the prev life.
Here she Said that she want Help for the succession but in His past life His Standing was a bit different so He could Not be Somebody useful to her.
Even so she used her unborn to marry him