Demon Lord's Reincarnation

Ren was familiar with this particular box, this was a box that was created during his rule. It was created for the daughters of demons with high social standing. These boxes were meant to be a toy and form of training for young daughters. 

It was a storage device that would only open when the right amount of mana was used. This was not only a popular toy for practicing mana, but it was also a nice place to hide one's belongings. The box was crafted using the bones of a monster that could deflect almost all physical attacks. It was also imbued with a spell that makes it hard to open for those that aren't bound to it. 

Still, for someone of Ren's level forcefully opening the box wasn't a problem at all. When Ren forcefully opened the box he saw that inside it was a diary. The diary was made from the skin of a manticore which meant whoever owned this diary was the daughter of a very influential demon.  

Ren opened the diary and started reading a random passage. 

"I was finally able to open the box daddy gave me. It took me a few months to figure it out which might have disappointed daddy. The nanny that takes care of me told me that other children younger than me could've done it in less time. I need to do my best so that I don't embarrass daddy." 

As Ren expected this diary was the diary of a little girl. 

"After I told daddy what my nanny told me he got a bit angry and fired the nanny. I asked why he did that, and daddy told me that my nanny was a bad person. Was she really a bad person? My nanny always told me wonderful tales about daddy and daddy's daddy. Still, if daddy said the nanny was bad then she must've been bad." 

Ren skimmed through a few pages as it was all about how she was struggling with her mana control. Ren decided to skip most of the pages and got to the middle part of the diary. It would seem that the little girl grew up a bit as her writing style changed.

"Today was the day I thought I would enroll in school, like most of the children. I thought that I would finally be able to make friends, to be able to leave the mansion and see a bit of the world. Unfortunately, father had other plans, he wanted me to be homeschooled." 

This time the girl started writing about her studies and how her father came to visit her less and less. As Ren continued to read on, he found it weird that not once was the girl's mother mentioned. Though there were multiple times the girl wrote about her grandfather. It was written that her grandfather was supposedly a man of great status. Ren was wondering who could that be, it might have been one of his generals. 

As Ren continued reading about the girl's worries, joy, and pains he felt it was weird. 'This girl feels less like a demon and more like a human.' Demon children wouldn't write such emotional things, and would most likely write about their exploits in seeking greater personal strength or political strength. Yet this girl wasn't that worried about such things, instead, she wanted to live free of her obligations. 

...

Ren was engrossed in his reading when he got to the part where the girl finally wrote something about her mother. 

"It was my fifteenth birthday and I was expecting to have a big party as it was my coming of age. Yet once again, father has denied me such a thing. I finally confronted him about my situation. I asked him why I can't show my face to others? Why must I be kept a secret from everyone else? I told him that I felt like a prisoner in my own home. When I told him all that, father decided it was time to tell me the truth about my birth. It turns out my mother was a human and not just any human she was a human hero. The reason I was hidden away was because I was half-human, but more than that, I was the daughter of the most hated enemies of demons a hero."

The girl was a half-human normally that would have only resulted in a little bit of ridicule but because her mother was a hero the situation was dire for her. While Ren was still the ruler of all demons there were many that had human spouses. Since humans and demons look almost exactly alike and their biological make-up was nearly identical they were able to mate and reproduce. 

Still, because of the ongoing war against humanity, some demons looked at humans as lower beings. Of course, Ren as Demon Lord Kretos tried to stabilize the situation, but ultimately he failed as he was someone more fit for war than handling such matters. Now if you were half-human then it was pretty much certain that you were a target for hate, but if you were a child of a hero then that made you a target for vengeance. Since at that time heroes were butchers in the eyes of demons. 

Ren continued to read the diary, the girl was now writing about how difficult it was to accept her human heritage. But as she grew older she finally accepted what she was. She could not blame her father for loving her mother. She couldn't blame the hate the demons felt for the humans, especially the heroes. So in the end, the girl simply accepted her position in life. As it was already a miracle that she was still alive in such a society. 

Ren finally got to the final passages of the diary. 

"Father has been meeting with some strange people from the alliance. I'm not sure as of now, but it seems like my father was about to commit treason." 

"I confronted my father about the shady dealings that he was having. He then looked at me and simply said that everything he was doing was for a better future. To make a world where I can live freely. He then whispered that this was a promise he made with mother." 

That was the final entry in the diary.