I don't really know how this would work, only that it'd be an interesting set of circumstances. Perhaps Ichigo could be a rival to Yuno and Asta, or perhaps he should work alongside the Wizard King. If taking the latter option, I think it'd be best if it went something like this: a post TYBW arc Ichigo was traveling through the Dangai back to the human world after having just beaten Yhwach. He falls through a gap in the Dangai after a series of unfortunate events, and he ends up in the world of Black Clover, where he meets the Wizard King. Prior to meeting the Wizard King, He figures out that his spiritual powers have been converted to magical powers, as well as that he has no way home. He then eventually acquires a Grimoire to help see just what aspects of his powers have changed and how to potentially develop them further. I would like for there to be a particular focus on his Quincy abilities in that case. Once he meets the Wizard King, he tells him the circumstances of who he is and how he arrived to this world, and the Wizard King takes an interest in him, but is also cautious of him. As such, he is put under direct employment of the Wizard King, a right-hand-man if you will, and becomes his friend and partner. To make things even more interesting, don't have him join the Black Bulls, or any of the various groups for that matter. Just have him help out from time to time and have him be there for any significant happenings that occur. Maybe, if you really want, you can even give Ichigo some powers from people he knows, like having Orihime's power of reality rejection. Alternatively, you could give him the abilities of whoever he has defeated, like Aizen's illusions, or even Yhwach's Almighty, though I think that might be going too far and making him too overpowered. If you want to take the route of giving him his enemies' powers, but don't want to give him Yhwach's Almighty, perhaps give him the ability to bestow shrifts to people.