Aizen Sousuke would be an interesting crossover character. Since he's so powerful and manipulative in the Bleach universe, seeing him in a different setting with Ichigo could create some really complex and intense storylines. They could be forced to work together against an even greater evil in a crossover universe.
Sasuke Uchiha from Naruto would be a good crossover character. Both are strong - willed and have powerful abilities. They could start off as rivals, each thinking their way of doing things is right. But as the story progresses, they could learn from each other and team up to face a threat that neither could handle alone. For example, a powerful demon that is immune to normal attacks but can be defeated by a combination of Ichigo's spiritual power and Sasuke's Sharingan techniques.
One interesting character to crossover with Ichigo is Light Yagami from Death Note. The clash between Ichigo, who is a protector, and Light, who is a morally ambiguous character with the power to kill, would be very engaging. Saitama from One - Punch Man could also be a great choice. Saitama's overpowered nature and Ichigo's journey to become stronger would make for an interesting story. And what about Alucard from Hellsing? His vampire powers and Ichigo's powers related to the afterlife would create a really dark and exciting crossover.
One idea could be Ichigo crossing over into a different anime universe like the Naruto world. He could meet Naruto and they'd team up against a common enemy. Maybe a powerful new threat that combines the powers of Hollows and the Tailed Beasts.
Another great character to include would be Saitama from One - Punch Man. His nonchalant attitude towards fighting, despite being extremely powerful, would be really fun to pair with Ichigo. Ichigo might be frustrated by Saitama's lack of excitement during battles, while Saitama could be intrigued by Ichigo's complex powers.
One great 'Bleach Ichigo Transcendent Crossover Fanfiction' is 'Ichigo in the World of Naruto'. It shows Ichigo's powers in a completely different ninja - filled world. His reiatsu stands out among the chakra - using ninjas. It's an exciting read as he has to adapt to new rules and also face off against powerful foes in the Naruto universe.
One possible plot could involve Ichigo's spiritual energy causing a ruckus in the DxD world. His power might be misinterpreted, and he has to prove that he's not a threat. At the same time, he could learn some unique abilities from the DxD characters, and they from him. For example, the devils in DxD might be interested in Ichigo's zanpakuto and its powers, while Ichigo could gain some knowledge about magic from them.
One possibility could be that Ichigo's unique powers as a Soul Reaper and his transcendental forms could create an interesting dynamic in the DxD universe. Maybe his Hollow powers would be seen as a new type of 'evil' power there, and the devils would either try to recruit him or fight him. Also, his Bankai and its evolutions could make him a formidable opponent against the various factions in DxD.
Maybe Naruto from Naruto could be a crossover character. His ninja skills and Ichigo's combat abilities could create some unique fight scenes. Also, their different ideologies about friendship and power could lead to some great character interactions.
Ichigo could meet Frodo Baggins. Frodo, being from a very different kind of world, would find Ichigo's situation strange. But they could bond over their shared sense of being out of place in some ways. Frodo could teach Ichigo about the importance of perseverance in the face of great odds, and Ichigo could protect Frodo from any potential threats in this crossover world with his swordsmanship.
Well, a common theme is exploring Ichigo's character development in a crossover. When he meets characters from other series, he might learn new ways of using his powers or gain new perspectives on his role as a protector. Another theme could be the clash of different power systems. For instance, if Ichigo crosses over with a character from a series with a completely different type of energy source, like chakra from Naruto. And there's the theme of friendship and camaraderie in a crossover fanfiction. Ichigo might form new bonds with characters he never would have met in his own Bleach universe, and these relationships can drive the story forward in interesting ways.
A good crossover character could be Naruto. He and Ichigo share some similarities in their determination and their growth as characters. They could team up in the new dimension, with Naruto's ninja skills and Ichigo's sword - fighting abilities making for an interesting combination against the new threats they face.