One great fanfic could be 'Reg and Riko's Adventure Beyond'. It beautifully captures their relationship as they explore deeper into the Abyss. The author does an amazing job of showing Reg's protective nature towards Riko.
A title like 'Riko & Reg: Unraveling the Made in Abyss Story in Fanfiction' would work well. It gives the idea that through the fanfiction, the story of Riko and Reg will be explored further, perhaps uncovering new aspects of their relationship or their journey in the world of Made in Abyss.
Archive of Our Own (AO3) is also a great place. It has a well - organized tagging system. So, you can easily find fanfics about Reg and Riko in the Made in Abyss fandom. There are often some high - quality and unique takes on their relationship there.
First, the unique bond between Riko and Reg. Their relationship is full of mutual support and growth. For example, Reg's mechanical abilities and his loyalty to Riko can be highlighted. Second, the dangerous and mysterious world of Made in Abyss. Describe the strange creatures and environments they encounter. Third, Riko's determination. It's a core part of her character and can drive the plot forward.
There are many possible fanfics for Reg and Nat in the Made in Abyss world. Some might focus on their adventures together exploring the Abyss. For example, a fanfic could be about them facing a new and dangerous creature while on a quest to a deeper layer.
A simple fanfic could be about Reg and Nat sharing a quiet moment on the surface, away from the dangers of the Abyss. They could be talking about their dreams and fears, getting to know each other on a deeper level.
One challenge is getting the tones right. 'Made in Abyss' has a very distinct, often dark and mysterious tone. When crossing over with another work, maintaining that tone while integrating the other work's elements can be tricky.
There might be a fanfic that focuses on the backstory of one of the characters, like Riko. It could explore her early days in the orphanage, her training, and how she developed her strong will to descend into the Abyss. This could give readers a deeper understanding of her character.