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.
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.
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.
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.
Akame ga Kill novel's plot is centered around the struggle between Night Raid and the corrupt powers. Night Raid is a group of assassins. Tatsumi's entry into this world of conflict is a significant part of the story. As the story progresses, the battles become more and more fierce. The relationship between different characters, such as the complex feelings between Tatsumi and Esdeath, also adds depth to the overall plot. There are also political intrigues and power struggles within the government that Night Raid is trying to overthrow, which makes the plot very engaging.
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.
One plot idea could be Leone discovers a hidden power within herself during a dangerous mission. This new power could be related to her animal instincts getting amplified. It might start with a near - death experience where she has to fight off a powerful enemy alone. Another idea is Leone having to form an unlikely alliance with a former enemy to protect the weak in the city. This would show her softer side and her sense of justice.
How about a plot where both Naruto and Mine are summoned by a powerful being who wants to test the limits of different types of warriors. Naruto and Mine are pitted against other powerful characters from different universes. At first, they are reluctant to work together because of their different backgrounds and ways of fighting. But as they face stronger opponents, they realize that they need to combine their skills. Naruto's Rasengan and Mine's Pumpkin could be used in a combined attack. And during this time, they also develop a friendship that transcends their different worlds.
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 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.