Another idea is a story where Akame somehow gets the power of the Nine - Tails. This would completely change the power dynamics in her world. She could use the power in unique ways, like combining it with her Murasame sword skills. And perhaps she would have to learn to control the Nine - Tails' power, just like Naruto did.
Well, it could be really exciting. Imagine Naruto's ninjutsu skills combined with Akame's swordsmanship. For example, Naruto could use his shadow clones to distract enemies while Akame sneaks in for a deadly strike with her Murasame. Their different worlds, one full of ninjas and the other with a more medieval - like setting of assassins and political intrigue, would create a really unique and action - packed story.
You could also introduce a new threat that both Naruto and Akame ga Kiru characters have to face together. Maybe a powerful demon or an evil organization that has the ability to manipulate both worlds. This would force the characters to work together, and you can explore how they adapt to each other's ways of fighting and thinking. In this way, you can create a story that stands out from the usual fanfictions.
In terms of interaction, Naruto's Rasengan could be a huge shock to the characters in Akame ga Kiru. They might see it as a powerful and strange form of attack. Akame's group could teach Naruto about the importance of a well - honed blade, something that is not as emphasized in the ninja world. Also, the different power systems could lead to some interesting exchanges. For instance, Naruto's chakra control could be compared to the way Akame and others use their internal energy. And there could be some cultural clashes too, like Naruto's love for ramen might seem very strange to the characters in Akame's world.
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.
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 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 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.
Sasuke and Esdeath could be a fascinating pairing. Both are extremely powerful and have a certain ruthlessness. However, Sasuke has his own moral code which would clash with Esdeath's more extreme views. This conflict could drive an intense story.