Strongest Survival by Otome Game’s Heroine (LN) - Vol 4 Chapter 5: Promise

Spot was summoned from his comfortable charging pad and familiar floors to a world of magic and intrigue. After the flight of his new patrons, he is left to care for a filthy castle. During his quest to keep this new home clean, he will face demons, foreign armies, and the dreaded stairs.All those who stand before him will be swept away. Those who follow his spotless trail will find enlightenment, purity, and a world on its knees.Follow this wholesome vacuum on his quest to power.

Xiao Ran transmigrated to a fantasy world. As a dungeon guard in the Celestial Dungeon, with a special floor called the Purgatory meant for powerful demons and martial arts experts, he faced a huge challenge from the start. The Eldest Princess acquired a forbidden martial arts technique and was banished to the Purgatory. However, no one was powerful enough to restrain her. All the dungeon guards were defeated. Xiao Ran stepped up and declared, “Your Highness, it’s better for you to behave yourself on my territory” and effortlessly subdued the Eldest Princess.

He progressed from imprisoning the Eldest Princess to delivering the Great Xia Kingdom from the evil clutches of various demons and evil martial arts experts.

…

Xiao Ran was the mastermind behind the scenes.

This is a story about a young man who sought to fight against his destiny. With the help from billions of Dragon Energies trapped on the Rising Dragon Pillar in his body, he emerged from the dark and quenched himself with the blood of ancient dragons. He fought the heaven with the Buddhist Art for the people he loved and built the Eternity Kingdom with his own hands. This is a story about the rise of the Martial Emperor who will rule both earth and heaven.

I finally managed to kill the demon lord.