Perhaps the werewolf OC is a former experiment of the empire. They escape and join the Night Raid. Their unique werewolf abilities, such as enhanced senses and strength, become a great asset to the group. They could have a story arc where they learn to trust the others and overcome their past traumas related to the experiments.
One idea could be that the werewolf OC is on a mission to protect a hidden village in the Akame ga kill world. The OC has to face off against the corrupt empire's forces while also dealing with the challenges of being a werewolf, like controlling their transformations during battles.
Another plot could involve the werewolf OC being from a long - lost tribe. They come to the Akame ga kill world in search of something. Along the way, they cross paths with the main characters. The OC's werewolf nature and the cultural differences from their tribe add an interesting dynamic to the story, and they might have to make difficult choices between their tribe's values and the new friends they make in this world.
To create a memorable werewolf OC, think about their abilities. They could have a special power like the ability to heal quickly. Also, consider their relationships. They might have a strong bond with one of the Akame ga kill characters, like Leone, because they both have a wild side. Their motivation is also important. Maybe they are on a quest for revenge against those who wronged their pack, which makes them determined and single - minded in their actions.
One idea could be that the OC is a new recruit in Night Raid. Leone takes the OC under her wing, and they gradually develop feelings through training together and going on missions. They could have a moment where they save each other's lives, which deepens their bond.
Maybe a plot where the magic in Fairy Tail is combined with the Imperial Arms in Akame ga Kill. Like, Natsu's fire magic could be used to enhance the power of an Imperial Arm. The Fairy Tail guild could also be in a conflict with the Empire from Akame ga Kill. This would lead to interesting battles and alliances between characters from both series.
Another possibility is that the Soul Reapers from Bleach are called to the world of Akame ga Kill to deal with a strange spiritual phenomenon that is related to the Imperial Arms. Some of the Akame ga Kill characters might have latent spiritual powers that the Soul Reapers help them discover. For example, Akame herself could have a connection to a Zanpakuto spirit that she has to learn to control.
Well, a great plot could be a school competition. Tatsumi and Akame are on different teams at first, but as the competition progresses, they find themselves drawn to each other. They start to secretly help each other out, which is against the rules. This causes a stir among the other students and teachers. And in the end, they might decide to forfeit the competition to be together, showing that their relationship is more important than winning.
One idea could be a crossover where Naruto and Sasuke are somehow transported to the world of Akame ga Kill. They could team up with Akame and the Night Raid members to fight against the corrupt empire in that world. Maybe Naruto uses his shadow clones to gather intelligence, while Sasuke's sharingan helps in combat against the powerful foes.
One idea could be to have characters from Rosario Vampire end up in the world of Akame ga Kill. For example, Tsukune could find himself in the middle of the conflict between the Empire and the Night Raid. His vampire powers might be seen as a strange and new force in that world. He could either side with the Night Raid, using his powers for good, or be forced to fight them due to misunderstandings.
Another idea is to mix the magic systems. The rings of power in 'Lord of the Rings' could interact in some way with the Imperial Arms from 'Akame ga Kill'. Maybe a character finds a way to combine the power of a ring with an Imperial Arm, creating a new and extremely powerful weapon or ability.
One idea could be to explore how Tatsumi and Mine handle the news of her pregnancy during the chaos of their fight against the corrupt empire. Maybe they initially worry about how their child will grow up in such a dangerous world, but then find hope in the idea of creating a better future for their family.
One idea could be to have characters from both universes meet in a strange, new dimension. For example, Tatsumi from Akame ga Kill could end up in the Highschool DxD world and have to adapt to the different rules and powers there. He might form an alliance with Issei to fight a common enemy that threatens both their worlds.