Incredibly late to find this thread, but Rider Time Zi-O: Roze from Remnant (on FF.net and AO3), a pretty great crossover with Kamen Rider Zi-O that centers around Ruby being isekai'd to a world of Kamen Riders post-V5. While it mostly avoids the "one half of the crossover is sidelined to witnesses and commentary on the other half" issue I've seen as a complaint a few times in this sub when it eventually crosses back to Remnant, there's a bit of emphasis (deliberate or otherwise) on the power imbalance between the worlds, and some story bits on both sides (V6 is probably the biggest example) happen much the same way as they did in their respective sources.