MTL - The 21st Century of the Gangsters Everywhere - ~ what if of UC ninety-six

Ukei Kaito fought a desperate struggle in order to fulfill his role as a summoned hero. He defeated the Demon Lord and saved the very world, only to meet an end filled but with betrayal. The companions that he’d trusted throughout his journey betrayed him and killed him by sticking a blade through his chest.

“Are you my knight?” The silver-haired youth looked at the blonde girl before him and asked, his cheeks flushed red. This was their first encounter when he was only ten years of age.

“Are you my bride?” He held her in his arms, embraced the girl who had accompanied him for ten years straight. He was sixteen years of age.

“Are you my king?” He knelt before the throne, smiling foolishly as he looked at the girl holding the sword victoriously. At this moment, he looked like the boy he was when they first met.

“I’m fine without having eyes for you. The entirety of Camelot is for your taking.” Smiling soft and gently, he gave his eyes to the girl who lost her eyes due to the curse of the red dragon. He doesn’t regret it, he thinks. He was twenty years of age.

“So… Arthur… Artoria Pendragon, are you willing… are you willing to spend the rest of your life with me?” His voice was soft and clear as he reached out to touch her hand.

This was their legend.

- Description from Novelupdates

Ning Yechen used to be the Demon Lord. He singlehandedly took over the Demon Realm and attacked the Heavenly Realm. His name preceded him throughout the Six Realms. He got tired of fighting, so he quietly went into seclusion and became a happy hermit.One night, an Empress from the Heavenly Realm fell into the Mortal Realm after someone drugged her with an aphrodisiac. She inadvertently fell into his room, and they made out. After the deed, the Empress quietly left. Just when he thought he would never see her again, she showed up in front of him ten years later, bringing a child, saying it was his daughter and demanding accountability from him! “She’s your daughter. You have to be responsible for us!” Ning Yechen was stunned!