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.
His story would become more complex. He'd have to deal with new powers and new responsibilities. His journey would likely take a different path as he explores the capabilities of the Arrancar Zanpakuto.
One great arrancar ichigo fanfiction is 'The Hybrid's Path'. It explores an alternate universe where Ichigo has more complex interactions with the arrancars. Another is 'Ichigo's Arrancar Ally' which focuses on an unlikely alliance between Ichigo and an arrancar against a common enemy. And 'Arrancar - Infused Ichigo' shows Ichigo with some unique arrancar - like powers.
In arrancar ichigo fanfiction, the exploration of identity is a key element. Ichigo has his own identity as a Soul Reaper, but when he gets involved with the arrancars, he may question who he really is. Is he still just a Soul Reaper, or is he becoming something more? Also, the power - up scenarios are common. Ichigo might gain new arrancar - based powers that are both a boon and a bane. For instance, he could have trouble controlling them at first. And the moral and ethical dilemmas are important. If he befriends an arrancar, how does he deal with the fact that arrancars are often seen as enemies by the Soul Society? These elements add depth and complexity to the fanfiction.
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.
I'm not entirely sure as it's a fanfiction, but generally in an Ichigo and Arrancar harem scenario, it might involve Ichigo having some sort of relationship with multiple Arrancar characters. However, without reading the specific fanfiction, it's hard to say exactly what the plot is.
Themes of forbidden love are quite common. In the Bleach universe, Soul Reapers and Arrancar are supposed to be enemies. So, a relationship between Ichigo and an Arrancar goes against the norms of their world. This adds an element of tension and drama to the fanfiction. Additionally, the theme of self - discovery can be present. Both characters may learn more about themselves through their relationship, especially in the context of this non - traditional relationship that is often the focus in 'ichigo arrancar lemon fanfiction'.
Love or at least a strong bond is also a common theme. It could be a romantic love or a deep friendship. Their relationship defies the normal boundaries between Soul Reapers and Arrancars. For example, they might fight side by side against a common enemy, which deepens their connection.