The transformation trope is often seen. Naruto could have a partial or full merman transformation. In the partial form, he might grow gills and a finned tail while still maintaining some of his human features. This could be used in battles to surprise his opponents. In the full form, he becomes a fully - fledged merman, which is not only great for underwater exploration but also gives him a unique advantage in water - based missions. And of course, there could be a love interest who is either fascinated or initially scared by his merman side.
One popular trope is the merman Naruto having enhanced underwater combat abilities. Since he has the merman bloodline, he can swim at incredible speeds and use water as a weapon more effectively. For example, he might be able to create powerful water currents or whirlpools with just a flick of his tail. Another trope could be the isolation aspect. Naruto, as a merman, might be shunned by some in the ninja world who don't understand his kind. This could lead to a story of him trying to prove his worth and find acceptance among his peers.
One common trope is the outcast narrative. Since she has a werewolf bloodline, the female Naruto is often seen as different and shunned by some in the village. Another trope is the power struggle. She has to learn to control her new werewolf powers which can be overwhelming at times. And of course, there's the discovery trope, where she gradually uncovers the secrets of her bloodline.
The Naruto's merman bloodline can greatly impact his relationships. If we consider his relationship with the village elders, they might see him as a potential threat or an asset depending on how they view his new abilities. They could try to use him for their own purposes, like sending him on dangerous underwater missions. With his peers, some might envy his unique powers, while others could be inspired by him. And when it comes to his family - like relationship with Iruka - Iruka might worry about Naruto being in a world that doesn't fully accept his merman side and try to protect him while also encouraging him to embrace his new identity.
The 'forbidden love' trope also often plays a part. Since Madara was once an antagonist in the Naruto series, their relationship in the context of a mpreg fanfiction can be seen as a forbidden or unexpected one. This can add an extra layer of complexity to the story, as they navigate not only the pregnancy but also the social and moral implications of their relationship.
Tenten is also a character that can be found in these types of fanfictions. Her weapon - based fighting style can be combined with a muscle bloodline ability, perhaps giving her the strength to wield even more powerful weapons or use them in a more unique way.
Another popular trope is the 'romance - centric' ones. There are a lot of fanfictions that focus on the romantic relationships between the characters, like Naruto and Hinata, or Sasuke and Sakura. They develop the relationships in ways that might not have been fully explored in the original series, adding more depth and emotion to the characters' interactions.
One popular trope is the 'Redemption Arc' for Konan. In many fanfictions, Naruto helps Konan move past her dark past with Akatsuki. For example, in some stories, he shows her the true meaning of peace, and she starts to fight for a better world.
One popular trope is the 'fish out of water' scenario. Hellboy suddenly finds himself in Naruto's world full of ninjas and strange customs, or vice versa. Another is the 'team - up against a greater evil'. They have to combine their powers and skills to defeat a powerful foe. The 'culture clash' trope is also common. Naruto's positive and energetic ninja culture clashes with Hellboy's more somber and dark world view.
One popular trope could be the mentor - mentee relationship. As mentioned before, Tsume could be a mentor to Naruto, teaching him things that others can't. Another trope might be the unlikely friendship. Given their different clans and personalities, their friendship could be an interesting story to tell.
One popular trope is the 'Enemy to Allies' trope. Since Scorpion is from the Akatsuki and Naruto is a Konoha ninja, they start as enemies. Fanfictions often explore how they can put aside their differences and work together. It adds a lot of drama and tension.
One popular trope is the mentor - mentee relationship. Tsunade often acts as a mentor to Naruto, guiding him in areas like control over his power or in understanding the politics of the village. Another is the adventure trope, where they go on an adventure together, facing various enemies and obstacles along the way.