One Piece : Roger Is My Vice Captain - Chapter 41 - Buster Call! ?

The tens of thousands of universes have merged. The disintegration of spiritual force led to the momentous collapse of the great Cultivation World, a mighty era that had endured through millions of years of history. In the wake of the large-scale invasion of the Wilderness, the Avalon of Five Elements has become the practitioners’ last stand.

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!

“If you were the supreme master of the Dao of Immortals, revered by countless beings, able to glimpse life and death, and understand the destiny, what kind of woman would you seek as a partner?”Jiang Feng: “I would marry an eighteen-year-old.”“...do you want to die?”“I'd rather die to marry an eighteen-year-old.”

[Vest flow, semi-invincible, Conan colleagues]

Interview with the protagonist:

Q1: What is your secret to becoming the ace shark player of the Black Organization?

Jiang Xia: “Take Conan to the target’s house for a walk.”

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Q2: What’s your secret to retrieving the treasures stolen by Kidd many times?

Jiang Xia: “His accomplice is my vest.”

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An interview with the detectives of Kexue World:

Q1: How do you view Jiangxia?

Detectives: “Except for solving the case too quickly + being unable to hold people back, there are no other shortcomings.”

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Q2: As a high school detective, why not join forces with Jiang Xia to fight against the Black Organization?

Detectives (hurriedly wave their hands): “No no no, can’t tell him that the darkness of the world is too heavy for him.”

- Description from novelbuddy