MTL - I Became Invincible After Sweeping The Floor For 70 Years - Chapter 189 explain

Humans across the world ended up joining a “Demon Kings and Heroes game”.

Several billion people were set down upon another world to act as “Demon Kings” and “Heroes”. Everyone has to chose their starting races from the start.

Zhang Nu was set in the Demon King camp.

He discovered that he could see hidden information that no one else could.
[Slime Demon King]. Low grade demon king bloodline… Not recommended!
[Kobold Demon King]. Low grade demon king bloodline… Not recommended!
[Dark Elf Demon King]. Mid grade demon king bloodline… Can be selected!
[Bloody Giant Demon King]. High grade demon king bloodline… Recommended!
[Abyssal Dragon Demon King]. Strongest starting bloodline… Extremely recommended!

When Fang Yuan was transmigrated into a world where Gu Breeder was the main profession, he found that he was not gifted.

Not only that, the Gu in his body could cultivate on their own.

[Your Iron Skin Gu has trained profoundly and has achieved the Gold-grade!]

[Your Bloodthirsty Gu has begun to multiply itself into a swarm of Bloodthirsty Gus!]

[Your Sunlight Gu has been absorbing the power of the sun for years and has gathered the Truth Flame of the Sun!]

[Your Drunken Gu has evolved into a Soul-reaping Gu. Your control over it has risen by 100 folds!]

[Your Flying Sword Gu was hurt in battle. Amid its desperation, it has evolved into a Sword God Gu!]

“Heck, even Gu undergoes involution as well now?” Fang Yuan let out a sigh.

A martial art expert from the Song dynasty lives like a Phoenix that can live again in another body after death. This time, he happened to take over the body of a Japanese high schooler who is also a victim of bullying and has a bit complicated family circumstances.

- Description from Novelupdates

God plucked one of his creations from his first Earth and gave him a second chance in another one of his Earths...surprise it is in DxD! Now reincarnated as a perverted side character how will our poor protagonist handle his new identity? Well he probably wont make the choices you will want him to, that's for sure!