Naruto: Limit Breaker - Chapter 303: Behemoth

Way, way, and very way before I was even born, my world was invaded. Actually, not just my world, my entire damn universe was overrun by another, led by a single race that called themselves the Eternals.And they were prepared. Very prepared. Every life we lost in the war against them was used by them. They didn’t just kill people, they captured their souls, forged them into Phantoms, and used the souls to twist beasts into Abominations. Our dead became their army.Three hundred years later, I was born. A guy with way too much energy. Sitting still? Impossible. Taking it slow? Not happening. I was always moving, always ready to burst into action. Then I awakened, and got a talent too.My Talent's Name Was Generator.Because of it I never ran out of energy. Ever. My muscles? Supercharged. My healing? Faster. My stamina? Please, I had no idea what being tired even felt like.So if the universe wanted to throw an endless war at me?Fine. I’d throw everything I had right back.I wasn’t born a hero. Never wanted to be one. But this war? It wasn’t just my universe’s fight anymore. It was mine. The Eternals made sure of that when they took my parents' souls.

As a precocious child, Lycoris suffers from a strange sense of deja vu. On the day her father told her about her fiancé, she realizes that her fiancé was a character from an otome game she once played in a previous life.

He rose from abjection and achieved eternity in glory.
He embraced the prettiest beauties and killed the strongest opponents.
He was able to shift the clouds into rain and cover the sky with one hand.
He could overrun the entire world and go anywhere as he pleased.
He pacified wars and held the world in awe.
He was matchless in the world.
However, his hair turned white overnight for his beloved woman and he was on the verge of death.
He was surrounded by enemies who were trying to take his life.
He struggled his way to become mighty and fought for everything he cherished.
For this age, he was the only king of the Dark World.
His name was a byword for might.
As a man living in the world, his only ideal was to pursue brilliance.

- Description from Novelupdates

You thought being reincarnated as an extra-side character was bad? Imagine being thrown into the body of a villain who is disowned by his own family and discarded by the author.