MTL - Reborn with an Old Enemy on the Day of our Marriage - ~ 61. Brothers can’t

In the world of dragons and snakes, the talented but congenitally sick martial arts master was reborn as the sole heir of the 19th-century Canadian manor owner. He thought he would make money by practicing boxing, but he took advantage of the industrial revolution to become a giant of the times. The opened template.

In the end, the original owner was a hopelessly sick and consumptive ghost! I am still a bastard having an affair with a gardener…

Wait, what’s up with the claw?

James Howlett looked at the bone claws protruding from between his fingers, and became more and more worried about his future.

- Description from novelbuddy

At dawn.The light of dawn lingered, hesitant to arrive, while the remnants of the setting sun had long faded into darkness. Within the city shrouded in thin mist, the hidden churches in the shadows, veins clinging to the cracks in walls, the gnawing sounds echoing from the sewers, and the murmuring shadows...A lantern bearer strolled forward.

Long ago a great calamity struck the earth, destroying much of it and merging what remained with pieces of other worlds.

With these worlds came Aether, a new form of energy that can allow one to transcend the bounds of normal mortality and human limitations.

In a world where humans absorb the essence of aether beasts to gain power, Aiden Hawke joins the class of humans known as arcanists, people who defeat aether beasts and absorb their essence into cores they forge within themselves, and who infuse themselves with the aether that permeates the world around them to increase the power of their body and mind.

However, unlike most, Aiden will find that he holds a unique gift and that his journey as an arcanist will not be so simple.

He is a young man without a spirit root. It is believed that this denies him the chance at cultivation. However, a mysterious lady imparts a Supreme Demon Classic to him and from then on, he starts his path of cultivation.
He undergoes a total transformation to emerge as the most fearsome and powerful fiendish demon in his era, that even immortals and fiends are fearful of him, and saints are at his beck and call.
Mastering the Supreme Demon Classic is the turning point in his life. He is able to unleash his immense and divine power from within, illuminating the entire universe!

- Description from Novelupdates