[macblo]

My headcanon is that each Heisei era season used to take place in its own continuity, save for Kuuga and Agito taking place in the same timeline. But during events of Decade, the multiverse just kind of "broke." Not only did this fuse the Heisei Era, Showa Era, and the Neo-Heisei era into one continuity, it also connected the Kamen Rider world with the Super Sentai world, which is also a shared continuity in my headcanon.

The connection wasn't strong at first but, over time, the world began to grow more and more connected until, by this time, they're basically two worlds stuck together, barely kept apart by a Dimensional Wall so thin that one could pass through it with basically no effort if there in the right place. Needless to say, Tokyo is one of those places.