How about a crossover with a more supernatural - themed horror like 'Hellraiser'? The Cenobites could cross paths with the Devil's Rejects. The Devil's Rejects' human evil could be a contrast to the otherworldly evil of the Cenobites. It could lead to a battle for dominance in the realm of horror or an unlikely alliance.
One idea could be a crossover with 'The Texas Chainsaw Massacre' family. The Devil's Rejects could team up with the Sawyers in some sort of mayhem - filled adventure against a group of bounty hunters. They could combine their unique styles of horror and chaos.
A crossover with a classic horror like 'Friday the 13th'. Maybe Jason Voorhees somehow stumbles upon the Devil's Rejects' territory. The Devil's Rejects, being the chaotic bunch they are, might initially try to take on Jason, but then realize they could use his brute force for their own evil plans.
Another interesting concept is to cross the devil fruits with the world of Harry Potter. Imagine a character with a devil fruit ability like the ability to turn into an animal (zoan type) trying to blend in at Hogwarts. They might have to hide their powers from the wizards while also using them to their advantage in the magical world, like using their animal form to explore hidden areas of the school.
A crossover with the Castlevania universe would also be cool. Dante could find himself in Dracula's castle, facing off against classic Castlevania monsters while also dealing with his own demonic foes. It would be interesting to see how he interacts with the Belmonts.
One interesting plot idea could be a crossover between the Devil May Cry universe and the Castlevania universe. The protagonist with Devil Trigger ability could find himself in the dark and haunted world of Castlevania. He has to use his powers to fight off the hordes of demons and undead creatures that are native to Castlevania. Maybe he teams up with a Belmont character and they exchange combat techniques and knowledge about their respective worlds.
One idea could be to have characters from different universes within the 'devil survivor 2' world meet and form unexpected alliances. For example, a group of normally opposing demon summoners having to work together to face a greater threat that endangers all of their worlds.
Ash from 'Evil Dead' would be a great character to include. He has experience dealing with all kinds of evil. The Devil's Rejects would likely see him as a threat at first, but Ash could end up using his knowledge of the occult to outwit them or, in an unexpected turn, work with them against a greater evil.
One idea could be that Pennywise from 'it' somehow enters the world of 'Devil May Cry'. Dante could mistake Pennywise for a particularly grotesque demon and engage in a battle. Pennywise, with his shape - shifting abilities, would constantly change forms to try and deceive Dante. Another plot could involve the characters from 'Devil May Cry' being lured into Derry by Pennywise's illusions. They then have to fight their way out while also dealing with the psychological warfare that Pennywise is known for.
One idea could be that Devilman and Devil Lady team up to fight a common enemy that is threatening both their worlds. Maybe a powerful demon from another dimension is trying to take over, and they have to combine their powers to stop it.
One idea could be a crossover with the Bayonetta series. Dante and Bayonetta could team up to fight a common, powerful demon. Their different fighting styles would make for some epic battles and interesting interactions. For example, Dante's flashy swordplay combined with Bayonetta's acrobatic and magical combat.
One idea could be that Naruto somehow ends up in the Devil May Cry world. He might mistake some of the demons there as similar to the tailed beasts he knows. For example, he could try to 'befriend' a demon in the DMC world thinking it's like how he dealt with Kurama. Another idea is Dante teaching Naruto some swordsmanship. Dante's flashy and powerful combat style could blend well with Naruto's own energetic fighting moves.
One idea could be Dante from Devil May Cry being summoned to the world of Devilman by Akira. Akira could seek Dante's help to fight against a new type of devil that is beyond his capabilities. Dante, with his arsenal of weapons and devil - slaying skills, would then team up with Akira in his devilman form to take on this new threat.