Who could be the main antagonists in 'ichigo is a vampire fanfiction'?

There could also be a powerful vampire hunter. This person might have a personal vendetta against vampires in general or specifically against Ichigo. They could use all kinds of weapons and tactics to try and kill him.

It could be some rogue shinigamis who oppose the idea of rukia and ichigo having a child together. They might see the baby as a threat to the existing power structure in the Soul Society.

In this fanfiction, the Church or religious authorities in Camelot could be the main antagonists. Vampires are often associated with the devil or evil in religious beliefs. So, they might see Merlin's transformation into a vampire as a sign of him being corrupted by dark forces. They would try to exorcise or destroy him, not understanding that he's still the same Merlin at heart, just with a different form and new powers.

Other vampires might be his main antagonists. They could see Issei as a threat, perhaps because he's a new vampire with different ideas or powers. Or they might want to use him for their own gain.

A group of vampire hunters could also be the antagonists. They might not be able to tell the difference between Issei and a full - blooded vampire and target him. They could be very zealous in their mission to wipe out all vampires and view Issei as just another one to be hunted down.

Another vampire, an older and more powerful one, could be an antagonist. This vampire might see Percy as a threat to his power or territory. Maybe he wants to either kill Percy or make him submit to his rule.

Perhaps a vampire scientist who is conducting unethical experiments on both humans and vampires. Ichigo gets in his way when he discovers what the scientist is doing. This antagonist could be using his scientific knowledge to create powerful and dangerous hybrids. He believes that he is creating a new and better vampire - human world order, but his methods are causing a lot of harm, and Ichigo is determined to stop him.

The vampire Authority could be antagonists. They might see Sookie as an abomination since she was a fae - human before being turned into a vampire. They could try to eliminate her to maintain the 'purity' of the vampire race according to their own rules.

In some fanfictions, a powerful Hollow could be the main antagonist. It might target Orihime because of her special powers and Ichigo has to protect her while also dealing with his new - found feelings for her. The Hollow could be constantly attacking them, trying to separate them.

Often, Aizen can still be a major antagonist even in time travel fanfictions. His schemes might extend across time, and Ichigo and Orihime have to figure out how to stop his plans that are messing with different timelines. Another could be the more powerful versions of Hollows from different time periods. They might be stronger and more menacing than the ones Ichigo and Orihime are used to in their original timeline.