Shadow monarch in DXD (Male ocxcrossover)

Prologue

(POV, Magnus Ashborn)
My name is Magnus Ashborn, and my life has been absolutely normal and quiet, I had very loving and caring father and a lot of friends, I hadn't even once questioned why they were shadows literally, but I didn't care, the problem for me was that I didn't have a mother because she died when I was very young, I had tried countless times to ask my father to tell me more about her, but he would always say I was too young to know about it. However, everything changed when I turned 25 years old. My father told me his whole story. To say I was shocked that day would be an understatement, but his next words shocked me even more.

Ashborn: my son, I believe that you are old enough and I can now leave you alone and go to meet with your mother, and be able to...

I didn't even let him finish his sentence and interrupted him with a very loud shout.

Magnus: FATHER HOW CAN YOU LEAVE ME ALONE?! WHY CAN'T YOU TAKE ME WITH YOU.

Ashborn: I understand your feelings son, but unfortunately you can't come because you have your whole life ahead of you and I have a job here in the underworld for you. Also, the fact that I want to meet with your mother is not the only reason for my leave. I got news from other fragments that a lot of powerful beings want to destroy or conquer Earth, your mother and I have to use ourselves to create the barrier which will not let them come here, by doing that not only we will get eternal rest but also be able to protect this world. However, you still have to be careful because the leaders of aliens and monsters will still be able to create dungeons with different monsters with different powers and if the dungeons will not be cleared, it will trigger dungeon outburst which will allow the monsters to leave their dungeons and come to earth to destroy our barrier to let stronger beings come here. Your job will be to watch over this world, keep your existence hidden and try to continue our lineage. When an heir to my powers will be born I will come to him as a spirit to train him to become the next Monarch of Shadow. If you want to know how to inherit my powers three conditions must be fulfilled. First of all, a person has to be my descendant. Secondly, he has to have natural affinity and talent with shadows and death but if the first condition is fulfilled, my descendants will have natural affinity to these powers, so this condition is not that important. Finally, the person has to undergo very strict training in the development of mindset, body and skills to become worthy of the powers of the Monarch of Shadows, the training has to be started around the age of 6. I didn't do this training with you because I didn't want you to go through it because I thought it wasn't that necessary considering how we lived and I wanted you to have a normal life, but now I regret that decision, so I am very sorry, that I made a decision without consulting you but you were very young and couldn't really comprehend that. I believe now you understand why you can't come.

Your mother and I will be watching over you from time to time when we will have an opportunity. Finally, thank you for being born and becoming someone I can be proud of calling my son!!

Magnus: Sobbing 😭, thank you for being a wonderful father and I hope you will be happy with my mother over there, and I am not angry at you because I understand everything now!

Ashborn: Smiling 😊, Good bye my son, have a good and happy life and thank you very much again!

Magnus: I will, don't worry. Good bye!

(Ashborn leaves)

( Time skip: 480 years later)

It was about 480 years after my father left. Nobody knew about his existence, he was a myth, but nobody believed that he existed. Also, as my father told me, dungeons started to appear all over the underworld, the main reason why devils could survive the sudden appearance of the dungeons after the war is the genius of Ajuka Beelzebub who created evil pieces and a device to measure the rank of the dungeons, which allowed to not risk of losing devil peerages. I came into contact with the new devil Satans and quickly became friends with them and for my backstory I said I was from a quite poor devil house which wanted to avoid war so we left very far away in the uninhabited area of the underworld to avoid extinction of the house but only I could escape the wrath of the of the Old-Satans so I was all alone without any family after very long lonely time, I met and married a very beautiful woman who had long black hair which was going down until her waist and a good figure, but the reason I fell in love with her was her kindness and motherly aura around her which I didn't have chance to feel when I was a child. Her name was Park Kyung-Hye. She changed my live completely and it was the happiest years of my life after my father left me.