Another aspect could be the origin of this Darkness Zanpakuto. It might be related to some ancient and evil force in the Soul Society that has been dormant for a long time. Ichigo's discovery of this Zanpakuto could be a sign that this evil is starting to stir again, and he has to figure out how to either destroy it or use it for good before it's too late.
The fanfiction could also explore how Ichigo's relationships change due to his Darkness Zanpakuto. His friends might be scared or distrustful of him. Rukia, for instance, could be torn between helping Ichigo master this new and dangerous power and being worried about the consequences it might have on him and those around him.
Ichigo might gain the ability to manipulate shadows with the Darkness Zanpakuto. He could use the shadows to hide, to attack from unexpected angles, or even to create illusions. This would give him a whole new set of tactical options in battles. He could also absorb the darkness around him to strengthen his attacks or heal himself, much like how he currently absorbs spiritual energy.
It could be a fanfiction that delves into the power dynamics. Since Ichigo has three zanpakuto, perhaps it shows how his power has increased exponentially. It might also be about the training he had to go through to be able to handle three zanpakuto, and how this changes his role in the Bleach universe.
One idea could be that the female Zanpakuto has a unique personality. For example, she could be sassy and constantly tease Ichigo while also being fiercely protective of him. In the fanfiction, she might have her own backstory, like being created from an ancient power that was sealed away for centuries until Ichigo awakened her.
It could completely change the dynamics of his powers and battles. Maybe a new Zanpakuto would give him unique abilities or force him to adapt his fighting style in unexpected ways.
Perhaps they are a gift from a mysterious and powerful being who sees Naruto's potential. This being could be observing the Naruto - verse from afar and decides that Naruto is the perfect candidate to wield dual zanpakuto. The being may have their own reasons, like wanting to see how Naruto will use the powers of two zanpakuto to change the balance in his world.
Sorry, I'm not sure of specific ones off the top of my head. But you can try searching on fanfiction websites like Archive of Our Own or FanFiction.net. Just type in 'Ichigo has 3 zanpakuto' in the search bar and you'll likely find some interesting reads.
Well, if Naruto had a zanpakuto in a fanfiction, it would completely shift the power dynamics. The zanpakuto has unique abilities in the Bleach universe. Naruto's existing jutsu and combat style would be blended with the new power of the zanpakuto. Maybe his Rasengan could be combined with a zanpakuto - based attack. It could also lead to new rivalries as characters from the Naruto world might be intrigued or threatened by this new power he wields.
Well, he might gain new and powerful abilities. In the fanfiction world, meeting one's real Zanpakuto could be a turning point. Ichigo could unlock hidden powers that were previously unknown to him, which would make him even more formidable in battles against his enemies.
One possibility could be that Female Ichigo brings a new perspective to Squad 4. Since Squad 4 is mainly about healing, she might use her unique skills in a different way. Maybe she combines her combat abilities with her newfound leadership in the medical squad. For example, she could develop new training methods for the members of Squad 4 to better defend themselves while also being efficient healers. This would make Squad 4 not just a place for healing but also a more well - rounded unit in the Soul Society.
The zanpakuto could have the power to breathe fire, just like a dragon. This would add a new offensive ability to Naruto's arsenal. He could use it in combination with his existing jutsu, like sending out a stream of fire while using his shadow clones to surround the enemy.