One common theme is growth. Both characters are often shown to grow as individuals and in their relationship with each other. For example, Mori Jin might learn more about patience from Mira, and Mira could learn about taking risks from Mori Jin.
One idea could be to cross Mori Jin with a character from a different anime like Naruto. Mori Jin could end up in the Naruto world and have to deal with different jutsus and the ninja way. He might even teach some of the ninjas his own martial arts skills.
Rimuru is more likely to win. He has shown extraordinary powers throughout the light novel. His ability to quickly adapt and his vast array of skills give him an upper hand.
Light Yagami from Death Note. It would be a contrast in characters. Mori Jin could find himself in the world of the Death Note and try to stop Light's plans, or they could form an unlikely alliance where Mori Jin tries to change Light's view on justice while also dealing with the power of the Death Note.
Among the main characters besides Rimuru are Gobta. He is a goblin who is rather comical at times but also shows growth throughout the story. Then there is Diablo, a very powerful demon who becomes Rimuru's subordinate. His power and knowledge contribute to Rimuru's rise in the world of the novel. There are also other characters like Milim, a dragonoid with a child - like personality who has her own impact on the overall plot.
One great Mori Jin x Mira fanfic is 'The Adventure Together'. It really delves into their relationship and how they support each other during different challenges. The story has some really interesting plot twists and great character development for both of them.
Milim Nava is an interesting character. She is a powerful Demon Lord with a child - like personality. She often gets involved in Rimuru's adventures in unexpected ways. Then there's Shion. She is a hobgoblin with great loyalty to Rimuru. Her over - the - top reactions and her growth in strength and character add a lot of fun to the story.
There's Veldora. He's a powerful dragon sealed within Rimuru's stomach at first. His presence has a great impact on Rimuru's growth and the story. Then there's Shion, a strong ogre who becomes one of Rimuru's loyal followers. She's known for her combat abilities. Also, Benimaru, a kijin, is an important character. He plays a key role in the development of Tempest.
Rimuru is very strong in the manga. He starts off with some unique abilities and keeps getting stronger through different events and encounters. His strength is not just physical but also in his strategic thinking and leadership skills.