You could also write a fanfic about the training days of a young God Eater. Show their struggles to master the God Arc, their relationships with their instructors and fellow trainees. It could be a coming - of - age story set in the God Eater universe with lots of action and character development.
Another idea is to set the fanfic in a post - apocalyptic world where the God Eaters have almost been wiped out. The remaining few have to find a way to not only survive but also revive their kind. It could explore themes of survival, hope, and the lengths one would go to save their species.
One idea could be exploring the backstories of the lesser - known characters in the Soul Eater world. For example, the story of how some of the minor meisters and weapons got to the Death City. Another idea is a 'what - if' scenario, like what if Maka and Soul never became partners? You could also create a fanfic where the characters have to face a new type of enemy that is not related to kishin eggs but something completely different, like an alien invasion of the Death City.
One idea could be an OC who is a weapon with a unique transformation ability, like turning into a musical instrument for a really different combat style. Another idea is an OC from a far - off land, bringing new cultures and fighting techniques to the world of Soul Eater. Maybe an OC who is a miester with a special power to communicate with the souls of inanimate objects and use them in battles.
One idea could be a story where the God Eater characters discover a new type of Aragami that has unique powers. They have to figure out its weaknesses and how to combat it. This could lead to new character developments as they struggle to adapt.
One idea could be that Ichigo and Maka meet in a dimension that is a blend of their two worlds. They initially mistake each other for enemies but then realize they have a common goal of fighting against a new type of evil that is emerging due to the merging of their universes. Another plot could involve the Soul Reapers and the Meisters exchanging their powers for a short time to better understand each other's fighting styles and learn new techniques. A third plot idea is that the Hollows in Bleach start to target the souls in the Soul Eater world, and the characters from both series must team up to stop this invasion.
A 'Tower of God Fanfic' could center around a forbidden romance within the Tower. Maybe between a Regular and a Ranker, which goes against the Tower's unwritten rules. This would create a lot of drama and conflict as they try to keep their relationship a secret while also dealing with the challenges of climbing the Tower and the political intrigue that comes with their different statuses.
In God Eater fanfiction, a cool concept could be time - travel. Imagine a God Eater going back in time to prevent the initial outbreak of the Aragami. This would change the entire course of the God Eater universe. Another concept is the exploration of different God Eater organizations. There might be fanfictions that create rival or allied organizations with their own unique cultures and combat styles. Also, some fanfictions might play with the idea of a God Eater losing their powers and having to adapt and survive in a world full of Aragami without their usual abilities.
One idea could be a fanfiction where the characters are transported to a modern-day world and have to adapt. For example, Maka and Soul having to go to a normal high school and deal with things like exams and social cliques while still maintaining their weapon - meister bond.
One idea could be to have the ponies from MLP enter the world of God of War. They could team up with Kratos and use their unique magical abilities to fight the gods. For example, Twilight Sparkle's powerful magic could be used to counter some of the dark magic of the God of War enemies.
One idea could be exploring Kratos' relationship with his son in more depth. Maybe show them facing a new, unexpected threat together and how they grow closer through it.
A God of War and Assassin's Creed crossover fanfic could be really cool. Picture Kratos in the world of Assassin's Creed, with his brute strength and combat skills clashing or collaborating with the assassins' stealth and parkour abilities. He might be on a quest that somehow intersects with the Assassin's Creed's fight against the Templars.