Well, it could be about Ichigo having some super - transcendent powers that he has to hide in the High School DxD world. Maybe he's a new student there and his powers start to disrupt the normal balance of the supernatural elements in the school.
He could fit in as a mysterious new student. His transcendent powers would set him apart from the rest. He might initially be seen as a threat by some of the factions in the school.
The story could then develop as Ichigo tries to find a way back home. Along the way, he gets caught up in the politics and battles of the DxD world. He might meet Issei and initially be at odds with him because of their different outlooks on power and combat. But as they face common enemies, they start to work together. Ichigo could also have run - ins with powerful devils like Sirzechs Lucifer, who might be intrigued by his power and want to either recruit him or eliminate him as a potential threat.
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.
Another aspect could be Ichigo's internal struggle in this new universe. He's used to the world of Hollows, Soul Reapers, and Quincy in Bleach. But in DxD, there are new moral and power dynamics. His sense of justice might be put to the test as he encounters situations that are different from what he's faced before. He might have to decide whether to interfere in the power struggles between the three main factions - devils, angels, and fallen angels - or stay out of it.
The characters in DxD would be quite shocked at first. Ichigo's appearance and his powers are so different from what they are used to. For example, Rias Gremory would probably be intrigued by Ichigo. She might try to form an alliance with him, seeing his potential as a powerful ally. Issei, being the main character in DxD, would likely be both jealous and in awe of Ichigo's abilities, and might challenge him at first but then learn from him over time.
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.
One great Ichigo High School DxD fanfiction is 'The Hybrid's Journey'. It combines the unique elements of both Ichigo's powers from Bleach and the exciting world of High School DxD. The story follows a new character who has a mix of both universes' traits and how they navigate through the challenges in this combined world.
In 'Twisted Fates', the plot twist is that the powers of Ichigo and a certain devil in High School DxD get merged accidentally. This leads to a new form of power that no one expected. It causes a huge shift in the power balance and makes both the allies and enemies of the characters scramble to adjust to this new situation. This fanfiction then delves into how they all cope with this unexpected development.
In RWBY fanfiction, a transcendent Ichigo can bring a whole new dynamic. He could potentially have powers that far exceed the normal capabilities in the RWBY universe. His sword skills, for example, might be on a level that no one in RWBY has ever seen. This could lead to interesting interactions with the RWBY characters, like Ruby being in awe of his combat abilities.