Tensei Akuma no Saikyou Yuusha Ikusei Keikaku

After being reborn as a low-ranking demon in the depths of hell, a former Japanese man named Kakyu spent two millennia honing his abilities until he became an unstoppable force. Just when he thought his fate was sealed in the brutal underworld, he finds himself cast into an entirely new realm. Embracing the chance to live a peaceful existence, Kakyu settles into a quiet village, cherishing the simple joys of life. But tragedy strikes when the village is ruthlessly destroyed before his eyes. Despite his desperate efforts, he arrives too late—only to discover a single infant, Alus, still alive amidst the devastation. Filled with determination, Kakyu vows to raise Alus with unwavering love and care, ensuring the child grows up to experience boundless happiness as a way of honoring the village that once sheltered him. What destiny awaits this unlikely pair in a world brimming with unknowns?

(Note: The rewritten version maintains the original plot and tone while ensuring uniqueness and expanding the narrative slightly for clarity and depth.)