You might be wondering, “What’s the demon lord being doing all this time?” Well, let’s start from the beginning. 

[Flashback] 

“Your majesty! Your majesty! I carry urgent news from the advisor.” A guard spoke to a figure in a regal throne. He came in a bit of a rush, but he took the time to exercise the proper measures befitting the figure in the throne. He bowed to the figure, not even daring to lift his head without proper permission. 

“You may rise. Tell me, what’s gotten you in such a rush? I heard you say urgent news came from the advisor. What’s the matter?” The figure asked. The guard finally raised his head to look at the regal figure in the throne. 

Red, long crimson hair covered the floor behind the throne. Hair that’d maybe give Rapunzel a run for her money. Skip the way too long hair and you’d find a face that enchants you. Long eyelashes covered the eyes of the regal figure and underneath them were bright orange eyes. His lips were as pale as his sheen milky skin. He wore a black attire that made him carry this melancholic vibe of someone who’d lost something they’ll never be able to get back. Just one sight of this figure was enough to make anyone, malicious or not bow before him, wanting to follow his every command, which is probably something only he can do. Just looking at him once is enough to put you under his control for all eternity, although he really didn’t like it. 

“Yes, your majesty. I’ll deliver the news right away. Advisor Charles has foreseen you being defeated by the next hero. He wishes for you to take precautions to stop your upcoming defeat. That is all, your majesty.” The guard concluded his errand. He bowed his head again. 

“Thank you. Tell the advisor to keep me updated on the next hero’s location. Oh, and thank him for me.” The regal figure didn’t forget to thank the guard. He waved his hand and the guard left. 

After the news he had just received, the king began to brainstorm. He had never had to deal with something like this happening before. All 374 heroes who have come to vanquish him were all dealt with swiftly, although they all came to the demon realm right after being proclaimed heroes, around 15. He didn’t know if it’d be the same this time. What should he do? What should he do? He thought for hours which turned into days, then weeks and he still hadn’t come to a solution. 

He was distressed over the news so much that he didn’t sleep the whole time, just a few breaks. He continued to think and think and then one day, while he was looking at the people of the city from a balcony, he got an idea. 

“What if I just make the hero my bride? That’d take care of everything. I’d conquer his heart and then make him mine. Once I've done that, I'll be the owner of the hero meaning that it wouldn’t really be a defeat even if I got defeated. It’s the perfect idea.” This idea he got from just watching a couple of his subjects from the balcony mingling around with each other. He began to enact his plan and called in the big guns. 

He contacted someone impartial. Heh, who am I kidding? She’s totally partial and utterly bored. He contacted the spirit of the world, the one who grants titles and abilities to all the creatures of this world. She would be the one to grant the next hero the title of Hero, meaning if he, the demon lord can get her, the world to actually acknowledge his plan, then it’d definitely work. He wouldn’t have anything to worry about other than coaxing his wife who’d be the future hero. 

The demon lord thought of many excuses to win the spirit over, like to unite the demon realm and make it greater or to save the poor people who’d be taken to the human realm to be used for who knows what if he’s defeated. He had a lot of them planned but fortunately, he didn’t need any of them. 

The moment he mentioned it, a gleam appeared in the spirit’s eyes. It was like she had met her savior. She hastily added it to her to-do list of granting abilities to people and then tells the demon lord that this plan would definitely work.  

She knew what she was saying. The demon lord did everything for his people and they were pretty happy with everything he did. He got rid of anything that’d destroy the lives of the people and they were happy. The spirit has been very pleased with the demon lord for so long that overriding someone’s destiny by adding something else to it was totally doable at current that she didn’t even play hard to fulfil this time and just granted his request. 

When it was finally time for her to grant the future hero, Marcel his title, she knew that he carried way too much pride and stubbornness when it came to the previous heroes, so she couldn’t blatantly place something that’d change his to-be destiny right in his face, so she sneakily placed it under the current one as a subtitle. She placed the title of Demon Lord’s wife under the Hero title. 

By placing it under his current destiny, his subtitle as the Demon Lord’s wife would slowly overlap with his previous destiny as the Hero and take over as the main title, overshadowing the Hero title in the process. It’d begin taking over once he enters the demon realm and when he finally meets the demon lord, I'd be complete. It’s the perfect plan. 

So, she placed his destiny as a wife under his nose and showed him his Hero destiny, which the hero didn’t take any time to embrace and begin to act upon. She covered her mouth and laughed slyly as she applauded herself for being so sneaky. 

She watched the hero grow. Although the wife thing was still a subtitle, it still made him unconsciously loyal to his husband the demon lord, so he became extremely dense when it came to the love department and he unknowingly crushed all the advances made upon him. The spirit didn’t know any more if it was just the boy’s soul accepting his destiny or just him being extremely dense. It was getting ridiculous. The hero roused love among the hearts of both boys and girls everywhere, but he unconsciously turned his back towards all of them, leaving everyone heartbroken. 

She just watched the whole time as he visited the dungeons and got more and more powerful and finally decided to head towards the demon realm, like a mother watching her son grow up the whole way. 

Meanwhile after the demon lord’s request was accepted by you know who, he began to make preparations to welcome his future wife. Although he was a king by all means, paying attention to anything other than ruling became an absurd concept to him. He always made sure to put the citizens first and so, he had a panic attack. 

He hadn’t been in a relationship before, nor planned to get married to anyone before this. He had been alone all this time for who knows how long that he didn’t remember if he had ever been in a relationship before. You can probably understand the panic he was feeling. 

He prepared so many things and gifts for the hero, but he didn’t know if they'd be to the hero’s liking. He’d pick this and then he’d worry about something and then he’d pick another and worry about something again. In the end, he wasn’t able to decide on anything, so he just had his servants pack them all up in a giant room. “Hmph, the hero can just choose what he likes himself when he arrives. I don’t have the time to bother with such trivialities.” He dismissed it like a tsundere, then he continued on with his duties. 

He was somewhat excited, at the same time nervous to meet his future killer, sorry, wife. He waited for six whole years when finally, the world notified him that the hero had arrived in the demon realm. On that day, he had a minimum of 5 panic attacks before he went to sleep.