It's also possible that Blake is a character who is given a new backstory within the Naruto fanfic. They could be related to an existing Naruto clan in some way, or perhaps they are an outcast with a mysterious past that gradually unfolds as the story progresses.
If Blake were in the Naruto world, she might become a ninja with her own unique skills. Maybe she could use her shadow abilities in a way similar to some ninja techniques. For example, her shadow could be used to surprise opponents like a ninja's stealth attacks.
Blake's character could develop by becoming more confident in her abilities. In the Naruto world, she would be exposed to different challenges that would force her to grow. She might start as an outsider but gradually become an important part of the ninja community.
Blake could be a mentor figure. In the fanfic, they might have extensive knowledge of a rare or forgotten ninja art and teach it to the younger generation of ninjas. For instance, they could teach about a special type of taijutsu that was lost in history. They would then guide the characters in using this new skill in their quests.
The fanfic might explore Blake's unique abilities and how they play out in the Naruto setting. Maybe there's a crossover of powers and teamwork.
One possible plot could be that Blake, with her unique skills from her original world, tries to adapt to the ninja world of Naruto. Maybe she joins a ninja team and uses her acrobatic and shadow - like abilities to help in missions. For example, she could use her skills to infiltrate enemy bases undetected, much like how ninjas in Naruto use their stealth techniques.
In most traditional Naruto and Blake storylines, Naruto has no relation to Blake as they belong to different fictional universes (Naruto and RWBY respectively). However, in some very creative fanfictions, an author might create a crossover scenario where Naruto could be made the father of Blake in a completely new and alternate storyline. But this is not a common or canon connection.
Blake's abilities, such as her acrobatic skills and her ability to use shadows, are quite different from the typical ninja abilities in Naruto. While ninjas in Naruto use chakra for jutsu like fireball jutsu or clone jutsu, Blake's skills are more physical and stealth - based. However, her shadow - like abilities could potentially be related to some of the more esoteric ninja techniques in the Naruto world that deal with illusions or stealth.
Blake and Leo are the protagonists. They might be friends or siblings who decide to embark on adventures in the Adventure Time world. Since it's a fanfic, they could have unique personalities and abilities that set them apart from the regular Adventure Time cast.
Perhaps an evil organization that wants to use the power of both Naruto and Blake for their own malicious purposes. They could be from a parallel dimension where they have studied both Naruto's world and RWBY's world. They would try to capture Naruto and Blake, forcing them to fight not only for their own freedom but also to protect the two universes from the organization's evil plans.
Maybe the plot could revolve around their combined combat styles. Naruto is known for his flashy and powerful ninjutsu, while Blake has her unique swordsmanship and shadow clones in RWBY. They could develop new fighting techniques together, like Naruto teaching Blake some of his chakra - based moves and Blake showing Naruto how to better use stealth in combat.