One plot idea could be a story where Tyki Mikk and Allen Walker are forced to team up against a common enemy greater than their differences. Maybe a new, extremely powerful Akuma that threatens to destroy both the Order and the Noah's side. This would put them in a situation where they have to rely on each other's unique abilities.
A plot could also involve a time - travel element. Allen Walker somehow travels back in time and meets a younger Tyki Mikk. Allen tries to change Tyki's future, to prevent him from becoming a Noah. This would lead to a complex web of interactions as Allen tries to influence Tyki's life without disrupting the time - space continuum too much.
Well, a possible plot for a Tyki Mikk x Allen Walker fanfiction could involve a situation where Tyki is injured and Allen has to take care of him. This could lead to a lot of tense moments as Allen is not sure if he can trust Tyki, but at the same time, he can't just let him die. Also, a plot could revolve around them being captured by a common enemy and having to work together to escape. Or perhaps a story where they both get transported to a different dimension and have to rely on each other to find their way back while also dealing with their own personal demons.
The character dynamics are often complex. Tyki Mikk, as a Noah, represents chaos and the side against the Order that Allen Walker is part of. But they can also find common ground in their shared humanity. For example, they might both enjoy simple pleasures like a good meal or a beautiful sunset, which can create a momentary truce between them.
To develop Tyki Mikk's personality in the story, you could focus on his hedonistic side. He enjoys the pleasures of life, so show how this affects his decisions and interactions with Allen. Maybe he tempts Allen with the allure of a more carefree life. For Allen Walker, his self - sacrificing nature can be developed further. He always puts others first, but in the fanfiction, this could lead to some internal conflict when it comes to Tyki. He might wonder if he should save Tyki or let him be because of his Noah nature. Also, Tyki's sense of loyalty, which is split between his Noah comrades and his newfound connection with Allen, can be a great area for character development. And Allen's ability to forgive and his moral compass can be tested and refined through his relationship with Tyki.
A crossover with the world of Fullmetal Alchemist would also be cool. Allen could meet the Elric brothers. His Exorcist abilities might be seen as a form of alchemy by some in that world. They could all work together to uncover a conspiracy that involves both the Homunculi and the Millennium Earl.
One great Tyki Mikk x OC fanfic is 'A Meeting of Souls'. It delves deep into the relationship between Tyki and the original character. The author does an amazing job of creating a believable backstory for the OC that ties in well with Tyki's own story in the original work. It has some really sweet moments of interaction between them.
First, you need to understand Tyki Mikk's character well. Read the original material to get a sense of his personality, his motives, and his backstory. Then, create an OC that can complement or contrast with him in an interesting way. For example, if Tyki is mysterious, the OC could be very straightforward.
One plot idea could be that the chibi Allen Walker discovers a hidden power within himself while on a simple mission. Maybe he stumbles upon a mysterious artifact that unlocks a new form of his Innocence. Another idea is that he gets transported to a parallel world where everything is in miniature like him, but there are different rules and he has to figure out how to get back. And also, a plot where he befriends a group of other chibi exorcists and they form a special team to take on a powerful Akuma that no one else could defeat.
Love and acceptance are also prevalent themes. The OC may come to love Tyki Mikk despite his flaws, and Tyki Mikk may learn to accept the OC's presence and the feelings that come with it. Also, power dynamics can be a theme. The OC might have their own power or lack of it compared to Tyki Mikk, and how they navigate that relationship in terms of power is often explored.
One idea could be that the reader is a new recruit in an organization where Renee Walker is a senior member. They start off with a bit of a misunderstanding but gradually grow to respect and care for each other as they work on various missions together. Maybe they have to go undercover as a couple in a dangerous situation and that's where their relationship really starts to develop.
One plot idea could be that the adopted Barry Allen discovers he has a unique connection to a parallel universe where his birth family resides. He then embarks on a journey to find out more about his origins while still maintaining his relationships in his adopted family. Another could be that he uses his speed - force powers in a creative way to solve problems within his adopted family, like preventing a family member from making a big mistake in time. A third idea is that an enemy targets him specifically because of his adopted status, thinking it makes him vulnerable, but Barry proves them wrong.