DIVINE BANE - Chapter 80: the birth of ARGUS

The world was consumed by a vile corruption brought from beyond – the sun dimmed, and life as we know it was almost extinguished.And yet it was not the end but merely the beginning.Long after the disaster, a lone survivor awakens with a newfound power to wield the divine flames and many questions about the past. He embarks on a long journey to burn the rot away, discover what's left of the old world and maybe, just maybe, ascend to divinity.

His Royal Highness the King of Han, who was afraid of the dark and ghosts and loved to cry, has always been the good baby of the princess.
Until one day, His Royal Highness the King of Han found a book in the bookstore…
Picture book?
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Search keyword: Protagonist: King of Han, Princess of Han

- Description from novelbuddy

Based on the popular Vocaloid series, by HoneyWorks, called “Kokuhoku Yokou Renshuu (Confession Rehearsal)“:

Natsuki, a third-year at Sakuragaoka High School, who holds unrequited feelings for her childhood friend, Yuu, who’s in the Film Club. However, instead of being honest about her feelings, she makes him be her confession “rehearsal” partner. Unable to say her true feelings, things start to get complicated when Miou and Akari, who are also in the Art Club, get involved! Will she ever be able to confess for real!?

Reborn into the world of Yugioh, it's natural if my goal is to become the best duelist!