A soul of a modern person finds itself in the body of a teen in Game of Thrones.
Luckily, the soul gets the foundation of Valyrians and creates one of the strongest Kingdoms in the history of the whole Game of Thrones.
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1) I do not like characters where one person destroys an army. So, Mc will be strong but not a Super Soldier King who slaughters on his own.
2) Mc will be king. In my opinion, kings can lead the army but kings should not battle.
3) No harem. Mc will marry only one person.