Deacon of Hell

Walking through the Gate, Momonga appeared inside a morgue, walking towards a corpse on a dissecting table. Looking at the familiar face, and his current condition, Momonga sighed at the weakness of humans. Was he this weak? 

Opening a Gate, Momonga brought the corpse to Hell and looked down at it. What he is about to do is an experiment, which is unknown if it's going to work. He wanted to use a race change scroll on the corpse but first he wanted to have a conversation with him. 

Reaching into his inventory, Momonga brought out a Wand of Resurrection. He was actually curious if this is going to work since Light Yagami is weak according to the standard of Yggdrasil meaning he will turn into dust if he was not strong enough.

Using the wand, green light flashes on Light's, before the god of the New World's finger's twitch and sits up, looking at the familiar face. 

Did the wand change or was Light Yagami actually strong? Well, I'm happy I didn't lose him. 

"Light Yagami, long time no see." Momonga said as a throne manifested under him and he sat down. 

Looking at Momonga, Light dusted his pants off and stood up. "So was Ryuk right, are you a S rank Shinigami? Otherwise the fact that I'm alive is hard to explain." 

'He, while dead, still remembers that lie I told?' 

"That was a lie, I'm not a Shinigami. Let me introduce myself again, my name is Momonga, the ruler of Paradise, Hell and the Human World. I was posing as a Shinigami because of some reasons, but that is no longer necessary." 

Light Yagami looked at Momonga with disbelief. He wondered what Momonga thought when he learned that he wanted to be the god of the New World. 

'Did Ryuk lie to me? Didn't he say Heaven and Hell did not exist.'

"I know you are confused, so let me explain. This place is the Shinigami Realm or it used to be. After obtaining this realm from the King of Death, I rebranded it Hell, and it took on the current appearance. Currently, all that exists in this realm is demons but it's still lacking. I brought you back, because I need something from you."

Lowering his head in thought, Light look a little surprised by the conclusion he came to,  "You brought me back because I have this something you want?...You want me to look after…Hell?" 

"That is correct, you are a talented human, it would be a pity to watch you fade into oblivion." It seems he didn't make the wrong decision, Light was indeed smart, Momonga thought. 

Light Yagami became lost in thought before agreeing. He didn't really have an option, because if he refused he would return to Hell. 

He failed to become the god of the New World, but he will become a god of Hell, though that title no longer matters. He had only sought to right the wrongs of the system and establish a perfect world, where no crimes exist, but he failed. 

"What does my job consist of? What are the limitations?" 

"Your job title will be Deacon of Hell, the highest ranking official of Hell. You are in charge of all the demons, you are to set up a system of punishment for the sinners that enter Hell in the future. You will determine what crimes warrant people to come here and you will find a way for souls to enter Hell. This will be your punishment for all the crimes you commit." 

Light Yagami's eyes twitched as he felt something was wrong. While it seemed he was gaining an exalted status as a ruler of a realm, his duties were too large. Not only that, just from the fact there is no system in place to have souls enter Hell, it was clear Momonga was using him as free labor. It's also possible the only reason he was even brought back was because of his intelligence, which was faltering.

Seemingly sensing that Light realized his trick, Momonga cleared his throat, not that he needed to, "Of course I will grant you privileges. Firstly, you will turn into a demon, which grants you supernatural powers and immortality. Secondly, you can enter and leave the Human World as you wish. Paradise will be out of the picture for now. You must gain complete control over Hell before being recognized as the god of Hell." Momonga looked at the unmoved Light before racking his brain, "I will grant you one wish, one within reason." 

Light Yagami poker face crack into a smiled, "I accept the deal. My wish is to kill everyone involved in my death." Shaking his head with a laugh, "Im joking, that would be low even for me. My wish is for an apple tree that never stop producing apples." A lonesome expression appeared on his face as if he was remembering something. 

Momonga knew why he asked for this but he didn't say anything. "Your wish will be granted. Also, for your residence, it will be in the center of Hell. Follow the Willow Tree and you will find it." 

Reaching into his inventory, Momonga grabs a black book with a smiling demon on its covers. This was one of the highest grade demon books, one that can turn one into an immediate level demon to a high tier demon. The higher the demon's grade, the more resources that are needed. 

"Light, touch the book. And repeat after me." 

Nodding, Light started to recite the incantation, "In the realm of darkness and dishonor, I call upon the abyssal embrace. Wings of sin, heart of hate, transform this mortal into a demon fallen from grace." 

Fire erupted from the ground and a black gate made from wailing souls appeared. Before anyone could process what they were seeing, a goat hand reached out and grabbed Light and the demonic book before shutting and disappearing.

Seeing the goat hand, shock appeared on Momonga's face as he didn't dare say what he was thinking. 

Clearing his mind, Momonga recites an incantation, "Summon Immediate Tier Demon - Hell's Warden!" 

A magic circle appeared on the ground and a demon appeared, looking exactly like Light Yagami with a couple differences. The demon had a head of red flame hairs, eyes of molten lava and skin red like scorch lobster. On his back are two demon wings and at the base of his butt is a long tail that moves around with a mind of its own. 

"Welcome back, I have a couple of questions to ask you, but for now, go look over your domain." Momonga gave Light a deep look and vanished, appearing in the skies, looking down at his newest servant. 

Looking at his hands and feeling the power surging through them, Light Yagami smiled, "It's good to be back." He felt there was nothing he couldn't do. There were many spells in his mind and he even had an innate ability that activated as a result of becoming a demon, Death Speech. 

He could kill anything by telling them to die. It was quite powerful as the demon god was surprised he had it, saying his son, a rare specimen of a demon, had the Command Mantra, which was similar but lean to command rather than death. 

With his strength, Light felt if he returned to the Human World, no one could stop him, well except Momonga but since he didn't interfere in his actions when he was human, he doubts he would now.

"It's a pity, the Human World is just a small world in the grand scheme of things, with my current power and status, my sense of justice will eventually reach this entire universe. When that happens, there will be no crime, no wars, just peace." His molten eyes shone oddly red, a hue many would be familiar with if they met the god of the New World. 

"Sadly, my ambition is no longer that." Light sighed and flew into the direction of the Willow Tree.

On the way, he looked at the spells in his mind and use them to understand their functions. 

Along the way, Light spotted many demons, some who reminded him of the demons from Dante Inferno. 

The demons upon spotting him, all knelt while placing their hands above their heads, not looking at him, which he imagined was a sign of obedience. 

He was not sure if this was because of his status or because of his power. If it's because of his status, everything will be easy, if it's because of power, that might be a challenge since he doesn't know how high his strength is ranked. 

While he believed Momonga gave him great strength, the strongest of the demons, without proof he couldn't move freely. 

Light was dressed in a black robe that covered his body except his face, wings and tail. His horns that curved into a crown made him look dignified. 

After what seemed to be years, Light saw a palace in the distance, but was not eager to approach and took his time. 

On his way, he learns a couple things about being a demon. Firstly, he was immune to fire. Even if he were to dip into a lava river, he would not be injured. Secondly, it seems demons do not require food or sleep. His stomach had not rumbled once and the need for sleep was absent. Lastly, it seems all demons or at least the ones I have seen, fall into the seven deadly sins. A demon will embody one of the sins. He for example embodied pride, which was obvious in retrospect. 

Inside the skies, Momonga looked at Light and thought, "I was not wrong, my friends do exist in this universe. Just like how I arrived in a world full of death gods, my friends must have arrived in different worlds. That hand belongs to Ulbert, there is no doubt about it. Unlike me, he must have arrive in a world of demons, otherwise his arm would not come through the door. Does this mean if someone uses a book of death to try to become a lich or undead, I will be forced to respond? An upgrade in responsibilities. Or did he simply get stronger?"