@Hungry Alien
I've been trying to come up with a good rival for Nero. It was either a human who had a demon arm as his replacement and trying to takeover his entire being slowly or an artificial half-breed created by some corporation attempting to create their own hybrids, but one of them proved unstable like Broly.
Any ideas?
I find it hard to create a rival for Nero. Nero is more of a "neutral" good guy. He is into action, but keep a cool head most of the time. It's hard to find an opposite personality which would be viable on the long run. Someone chaotic and destructive won't do because he would most likely destroy himself quickly.
For the rival relationship, both side need to be involved. But Nero never involved himself personally into something else than Kyrie, Credo and his job. So the rival will need to do something in order to involve Nero with himself on a personal note or have a link with the Order of the Sword. I also think that since Nero think with logic, having a religious rival linked to the Order of the Sword and working for it fanatically would be an interesting contrast.
With all of that said, I propose a former member of the Order of the Sword. He would know Nero even tho Nero doesn't know who he is for a simple reason : Credo and Kyrie. He would be another orphan turned into a brilliant knight by Credo, but unlike Nero who never took the order seriously, the rival would have devoted his life to the Order. Having no family at all beside the Order, he would have grown without love (unlike Nero), and became more violent and fanatic as a result. He would also have fallen for Kyrie, but due to his condition, Credo would have stopped any attempt for him to approach his sister. I would add that he had one chance, but Kyrie rejected him because she already had feeling for Nero and he ran away before she could say anything. This would be the final step to push the rival into a sinister fanaticism, training relentlessly and hunting down any target given. Seeing Nero with Kyrie would give the rival resentment for Nero and cause confusion on how Nero came to attract Kyrie's attention.
All of this dedication would have been noticed by Agnus who then asked Sanctus to assign the rival to him in order to bring him demons. During his time with Agnus, he would be the one who brought the Devil Arms used to create the false Hell Gates, showing a unparalleled genius for combat as a human. The time passed with Agnus also gave the rival important knowledge on demons, but he never took part to the Ascension ceremony because of his personal pride. Considering relying on demons power a cheap and unreliable way to gain power, he refused the offer and preferred to rely on his skill and training.
He would also firmly believe in the legend of Sparda, and would search to become a protector of mankind against demons just like Sparda was. But his loneliness and loveless life would slowly erode his feeling for others, becoming fully focused on destroying demons.
The fall of Sanctus would not affect him that much. It would mostly reinforce his believe that demonic powers bring no good. But it would show him that humans using demonic powers are a threat, and thus he would add them to his target lists, starting to search for sorcerers and "purging" them. After the dissolution of the Order, he would become a demon hunter and live from that. Also I would add that during this time, he would stumble into an unknown form of power, not from demonic source, and start using it, this power being potentially linked to a new realm introduced later.
After the event of DMC 5, demons are known from the public. The rival would keep on with his works, but more people would try to master demonic sorcery. This plus the credibility he now has and his efficiency at dealing with demonic threats would slowly attract people to the rival, causing him to form his own group of devil hunters in order to improve his quality of work. He would be able to share some of his power with his acolytes, causing them to have strange power as well.
And at last, for the confrontation with Nero, I would have the two on the same mission and meeting after defeating a big demon. The rival wouldn't recognize Nero at first, but would attack him because of him being an demon/human hybrid. After a fight, Nero, not wanting to fight an human, would push back the rival and escape, causing the rival to track him down with his group. Once at Nero's place, the rival would notice Kyrie, and then recognize Nero, causing his deep resentment to resurface.
That's it for now, I will probably add what power I would give to the rival and how he would look later, but I'm off to sleep for now.