Overlord (WN) - Volume 1 Chapter 4

Waking up again in his seventh reincarnation, prince Jing Beiyuan found himself back in time, when everything had yet to be set in motion. Having been given a second chance, Beiyuan had to survive court and decide whether it was finally time for him to let go of his feelings; all while trying to handle the youthful, innocent force of nature who had suddenly barged into his already complicated life.

- Description from Novelupdates

Protagonist travels between different anime worlds to right wrongs and uncover his reason for being along the way.

He, without doubt hates her.
What did she do to deserve his hate?
The person who she treated well like a brother did not even bother to notice it...

Years passed…

He needs to get married.
He needed a wife.
So she offered herself.
It was a marriage that will benefit both parties he said.

[The false necromancer has insufficient soldiers and is being ostracized and hunted. ]

[The real necromancer, countless skeletons, become the overlord of one party. ]

After Wu Heng obtained the double portal, he discovered that the original world was full of zombies.

When a gangster’s plan fails, another plan to survive begins.

Wu Heng chose to become a ‘Necromancer’.

Is it not allowed to summon the undead from another world? In the last days, the entire planet is a source of soldiers.

Can’t survive in the zombie world? Then I will live in another world and learn skills.

From then on, an undead army equipped with modern weapons appeared in the world.

Natural disaster strikes, millions of skeletons.

Immortal Bone Dragon, King of the Undead.

(Double portal + necromancer + magic + fantasy world + undead natural disaster.)

- Description from novelbuddy