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.
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.
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.
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.
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.
One great example could be a fanfiction where Ichigo's female Zanpakuto has a unique backstory. Maybe she was once a powerful spirit who chose Ichigo as her wielder because she saw his potential for great good. Another example might involve the female Zanpakuto having a different form of communication with Ichigo, like through dreams or symbols only he can understand. There are also fanfictions where the female Zanpakuto has her own set of powers that are not fully explored in the original series, and these powers play a crucial role in helping Ichigo during battles.
Perhaps in this fanfiction, Ichigo could cross over to a world where zanpakuto are living beings that can freely interact with their owners outside of their sword forms. His relationship with Zangetsu could take on a whole new dynamic as they explore this new world together.
One interesting concept could be Ichigo having a zanpakuto with entirely different abilities than Tensa Zangetsu. For example, it might have the power to control elements like water, which would change the way he battles. Another concept could be a zanpakuto that has a sentient form that is completely unrecognizable from Zangetsu, with a different personality and set of motives.
Well, he'd probably have a very different fighting style. The Arrancar Zanpakuto might have unique abilities that are more in line with Hollow powers. He could potentially have enhanced speed and strength, and the release form might be something really wild, like a combination of his Shinigami and Hollow forms.
Since Naruto is full of energy, the Zanpakuto could have a constantly vibrating or pulsating appearance. The scabbard could be orange, like Naruto's jumpsuit. And the guard of the sword could be shaped like Naruto's hand with a Rasengan formed in it. This would be a unique and eye - catching design that would clearly show the connection between Naruto and the Zanpakuto.