I'm not sure if there are a lot of such fanfics out there. But it could be an interesting concept. Maybe in this fanfic, Mifune, with his samurai skills and honor, imparts unique combat and life lessons to Black Star. It might show how Black Star grows under Mifune's guidance, both in terms of his fighting abilities and his understanding of the world around him.
Maka would also be a great character to interact with Mifune. As a strong - willed and intelligent student at the DWMA, she might be intrigued by Mifune's skills and his different approach to combat. She could try to learn from him, or even teach him some of the DWMA's ways in return.
In many Black Star fanfictions, his relationship with the other characters is a key aspect. He might have interesting interactions with Maka and Soul. Maybe there's a fanfic where they team up for a special mission and Black Star has to learn to work with them in a different way than he's used to.
A good fanfic about them should focus on their unique relationship. Black Star's over - the - top personality and Tsubaki's more reserved nature create a great dynamic. For instance, a fanfic could play on how Black Star's boasting sometimes annoys Tsubaki, but she still stands by him.
One great fanfic could be where they go on a mission together that's not part of the main story. They might face a new type of enemy that tests their bond and abilities in different ways. For example, they could encounter a demon that can split into multiple forms, forcing Black Star to rely more on Tsubaki's unique weapon forms than just his own strength.
One idea could be that Black Star leaves to pursue a solo mission to prove his strength without relying on his friends. He might encounter a powerful and mysterious foe that challenges his very core beliefs. This would make for an exciting story as he battles not just physically but also internally.
The theme of friendship also shows up a lot. Despite his brash exterior, Black Star has friends. Fanfictions may show how his friendships are tested, for example, when he has to make a difficult choice that could potentially harm a friend, and how he navigates through that moral dilemma.
Maybe Mifune's code of honor clashes with the more chaotic and rule - bending nature of some of the Soul Eater characters. For example, he might not approve of how Black Star is so eager for glory and fame without following proper protocol. This could lead to interesting character development and story arcs for both sides.
In a fanfiction where Black Star becomes a weapon, his design as a weapon would probably be very unique. Given his love for being flashy and his ninja - like style, he could be a weapon that has a lot of sharp edges and a sleek, black design. Maybe he'd be a sword with some sort of special ability related to his ninja skills, like being able to disappear and reappear during combat, or having the ability to cut through dimensions.