Another plot twist might be that the power of the Super Saiyan in the Highschool DxD universe has some unforeseen side effects. Maybe it attracts the attention of a new and extremely dangerous enemy that no one in the DxD world has ever encountered before. This would add a whole new layer of conflict and danger to the story.
In some fanfics, a great plot twist is when Ichigo's Hollow powers are misinterpreted by the DxD characters as some sort of devilish power. This leads to a lot of misunderstandings and conflict at first. Another interesting plot twist can be when Ichigo somehow ends up being related to an important figure in the DxD world through some convoluted backstory.
Well, one interesting plot twist is when the Nine - Tails in Naruto is somehow linked to a powerful devil in Highschool DxD. Imagine the chaos and new power - sharing or battling that could occur. It completely flips the script on how we see both the Naruto and Highschool DxD elements. Also, there could be a plot twist where the power - leveling system in Highschool DxD is reversed for Naruto characters, making them struggle in a new way and forcing them to adapt in unexpected ways.
Well, in these fanfictions, a common plot twist is the revelation of a unique ability. Say, the OC dragon hybrid can communicate with all types of dragons, which gives them an edge in battles and negotiations. Sometimes, the plot twists involve relationships. For instance, the OC might be betrothed to a powerful character without their knowledge, and this creates a whole lot of drama. And then there's the plot twist where the OC's dragon side is suppressing a dangerous entity, and when it's released, it changes the whole story dynamic.
First, you need to fully understand the settings of both Highschool DxD and the Super Saiyan concept. For the plot, you could start with the OC (Original Character) being a transfer student in the Highschool DxD world who has the power of a Super Saiyan. Then, you can create conflicts like how the OC deals with the different factions in the DxD world while hiding or revealing their Super Saiyan powers. Another idea is to have the OC's Super Saiyan powers attract the attention of powerful beings in the DxD universe, leading to various challenges and alliances.
One possible plot twist is that the hogyoku from Bleach somehow ends up in the hands of a character in Highschool DxD. This could lead to a character attempting to use it for their own gain, perhaps to gain ultimate power over both the devils and the angels. Another interesting plot twist is that a character from Highschool DxD gets reincarnated as a Soul Reaper in Bleach. They would have to learn the ways of the Soul Reapers while still retaining some of their previous abilities and memories. This could create some really interesting character development. A third plot twist could be that the balance between the three factions in Highschool DxD (devils, angels, and fallen angels) is disrupted by the arrival of Hollows from Bleach. The factions would have to figure out how to deal with this new threat, and it could lead to some unexpected alliances.
One interesting plot twist could be that Fem Harry Potter, with her magic skills, ends up changing the power dynamics in the Highschool DxD world. For example, she might introduce new spells that disrupt the existing balance of power among the various factions. Another could be that she has a hidden connection to one of the powerful characters in Highschool DxD, like a long - lost relative or something. This would lead to a whole new set of relationships and storylines. Also, perhaps her presence causes the different species in Highschool DxD to reevaluate their views on magic, as her magic might be different from what they are used to.
One interesting plot twist could be Naruto having to adapt to the unique magic system in Highschool DxD. Since Naruto has his chakra-based powers, seeing him struggle or find new ways to use his skills in a world of magic would be cool. For example, he might combine his shadow clone jutsu with some DxD magic to create a new and powerful technique.
One way to incorporate different Saiyan forms is to base the transformation on the power - up systems in Highschool DxD. In DxD, characters often gain power through training, contracts, or special items. You could make it so that a character has to collect a certain number of dragon balls (in a fanfiction - inspired crossover way) to unlock a new Saiyan form. Or they might need to make a pact with a powerful being in the DxD world to be able to access Super Saiyan 3. This way, you blend the two universes' power - up mechanics in an interesting and unique way.
First, you need to understand the basic elements of both Highschool DxD and the Saiyan concept. Incorporate the Saiyan's power and battle - thirsty nature into the Highschool DxD world. Maybe your OC Saiyan could be a transfer student who surprises everyone with their superhuman strength. Then, think about the relationships they will form. Will they be friends or rivals with the existing characters? Also, consider adding some unique Saiyan - related plot twists, like a special transformation that is triggered by a certain event in the Highschool DxD universe.
One possible plot twist could be that some of the devils in Highschool DxD turn out to be immune to the zombie virus due to their demonic nature. This could lead to a power struggle within the group as they decide whether to help the humans or use the situation to their advantage.