It would have been nothing if he was in pristine condition but there is a small crack in his soul that created a vulnerability within him. So the damage is more than nothing, but it still isn't a lot. He is made of much tougher stuff. He can deal with it.
The physical damage on the other hand is more than a little. His body is broken apart, crushed under the force of the explosion. He is missing more than 80% of his body part. The remaining parts of his body are just his spine, some ribs, and his skull. Even his skull is caved in. As serious as it may look, he is actually alright. He is alive and he is healing. He will recover if given time.
He was thinking about how the demons had exploded. It smells of treachery. Demons can't cause their bodies to explode unless they have physical organs that will allow for it. So unless all 12 demons with different sins, races, and features have organs that can allow them to explode or something is acting on them to cause the explosion.
He was lying helpless on the ground when a figure made of sin energy began to form beside him and this time, he can't move away. He has to watch the entire process of the demon lord creating her sin avatar.
"Come to gloat?" Aeternus asked her.
He doesn't feel any pain in his body, only a slight twinge in his soul. His body is healing rapidly due to his infinite chaos energy and she can't do anything to him with her sin avatar so he is in a good mood.
"No." She answered smugly. "I've come to offer my assistance."
Her sin avatar might just be a harmless manifestation of her will, but Aeternus found its presence unbearable right now.
Aeternus would have snorted if he could. He can't, so he made sure to transmit his feelings of derision over the mental communication.
"As you can see, I don't need your help."
"Are you sure about that?" She asked.
"Yes."
"We'll see about that." She seemed content to wait.
"Go away. I defeated the ones you sent to kill me. They failed."
"Oh, not at all. I don't think they failed. I think they did their job perfectly."
It was Aeternus's turn to be confused. "What do you mean?"
Even as he asked that question, he was beginning to have a feeling of dread. More danger was coming.
The figure smirked at him. "Can you feel it now?"
Yes, he could. Even more than that, he could see it. A group of 300 high-rank demons is flying toward him.
He sighed and said, "So you didn't lie to me."
"Nope. I only exaggerated a little."
These are not the dregs of the demon Hierarchy but the top dogs. The ones in charge of fortresses. They considere Aeternus a threat and his streak of visiting fortress after fortress only to loot and burn it down got on their bottom line. It is obvious that he wasn't doing it for access to an abyss altar but only for the fight. It meant he could come for them one day and their division would act against them.
They were afraid of him, but they weren't rash. Aeternus is already this powerful as a mid-rank demon, if he evolves then he will become a tyrant over them. That means they can't let him evolve and they can't fail their attempt at killing him. If they leave him and do nothing, there is still a chance that he wouldn't come after them. But if they attack him and fail, then they are doomed for sure.
So in a rare situation of compromise and a unified agreement, they formed a truce and created a task force to kill him. The task force was created with every demon in charge of a fortress. It was easy to do than expected because no one really trusted the truce and the contract they signed to that effect. They would prefer if all of them left their fortress at the same time and hunt Aeternus.
Their large number would make killing Aeternus all but certain and if they fail, then they will bear the consequences together. Never has a situation like that happened. The closest to it was when high-rank demons agreed to stay out of the last fight for power in the plane. This time, they formed a task force to kill a single demon who is oppressing them.
But Aeternus suddenly started escaping. He had somehow gotten word of their attack and started rushing toward the domain of mid-rank demons. They were confused for a while until they remembered that he is still a mid-rank demon and it may possible for him not to have sin energy sickness in an area of lower sin energy concentration. Now that things have gotten to that stage they can't let him escape. They rushed after him and have been chasing him for 5 days now.
"We are almost there now. If we don't catch up to him then we are in big trouble." One of them said.
Another one shouted at him. "We know that. Stop reminding us of our grim future."
Then one of them spotted a skull with smoke pouring out of it into the surroundings. They don't see the sin avatar standing beside the skull. Their perception isn't enough but what they saw is good enough for them.
"Is that the Ominous Reaper?" She asked the others.
They strained their senses and inspected the skull.
Someone said with glee, "It really is him and he is wounded."
Not all of them were fast enough to keep up with the group, so more than half of them were left behind. They had been worried that their number won't be enough to kill the notorious Ominous Reaper. It is an absurd thought that 300 top-notch high-rank demons won't be able to kill one mid-rank demon but it was a real fear for them. But it looks like they needn't have worried.