Toaru Majutsu no Index: New Testament - Volume 7, Epilogue: Once It’s Over. to_the_Main_Line.

Unhindered in the Demon Domain, the king is solitary!

In the world where immortals and demons strive, a good natured fellow sought the Demon Dao in search of justice.

At the end of his journey, he had eventually become this generation’s Heavenly Demon Emperor.

Although I am not fond of slaughter, I do not dislike it!

Desiring to see the Demon World, this is how I strive, this is how I become the Peerless Demonic Lord!

- Description from Novelupdates

In the year 3000, the Earth shattered and it was torn open by a rift between realms that unleashed ancient beasts, magical chaos, and apocalyptic storms. Civilization crumbled, giving rise to a brutal new law: Tame or be Torn Apart. Beast Tamers, bonded to mutated and other creatures now rule what remains of the world through strength, savagery, and guild-driven power.Kelvin, a scavenger scraping by in the ruins, lives in the shadow of these warlords until he unearths Xerion, the End-Tyrant, a legendary primordial beast sealed beneath the earth. Bound by a forgotten bloodline and a cursed contract, Kelvin inherits the Sigil of the Overlord, thrusting him into a war-torn world where survival is no longer enough.He was hunted by guilds, worshipped by outcasts, and pursued by enemies both human and monstrous, Kelvin must rise from nothing to either unite or destroy what’s left of civilization. As forbidden powers awaken and ancient truths unravel, one man and his beast stand poised to reshape the fate of a world teetering on the edge of annihilation.

He became stronger, faster than anyone else… but he lost. In the end, there was only despair for Kim YuWon.

In his last moments, he was given another chance… Through the sacrifice of his comrade, his fate had not been sealed yet.

Returning back to the past, he attempts to climb the Tower again with his unmatched talent.

To fight the ancient evils that threatens to destroy the Tower.