As I promised. I make this story.
The Old One of DxD. In brief summary, it was a story' of an Old One reincarnated into a half-blood devil in the DxD universe.
https://dynamic.webnovel.com/book/26755941206385005?utm_source=writerShare&utm_campaign=4319204064
This will be my project until I can create a broader story' board for my Gate fic.
I hope you enjoy it.