Not helped that the characters we followed through the series was a loser trying too hard to be the "Aloof badass" cliche and ended up being an unlikable dick, a girl who tried to justify Decade actions and claim him as a nice guy despite him being Tendou levels of asshole with none of the skills to justify the ego, and a genuine nice guy who got turned into comic relief and actually tended to connect with the AU riders a lot more solidly than Tsukasa...

Decade is a train wreck that didn't understand what it wanted to be, pulling the strings at what made other Rider series popular and assuming that stitching together their popular points and making the main protagonist the "Bad boy" character rather than the secondary rider would result in a success (Not commenting on the anniversary aspect because I could write a book on why that failed).

I'd read it.

I dont need to. I think I have the exact same book already in my head :lol

I would also like to read a book on that as well.

I would think that the Battle fight would be able to span multiple universes. In my mind, it's between two beings left, so it would continue based off of that, no matter the dimesnsion.

Although I wouldn't know how that Battle fight would affect other AU worlds' battle fights. But I think for an intial Battle fight in a world to start it needs a stone to kick it off so Kenzaki wouldn't just by being there.

Sounds like Super Megaforce.

Looks like I need to find a publisher for my upcoming book :lol

That's why I gave it the benefit of the doubt and assumed the original Kenzaki existing in Decade's universe wouldn't start another Battle Fight.
However, that doesn't explain away Hajime now being the lone Undead in the original Blade universe and the havoc that should be going on there.

What's to say that Hajime didn't universe jump with him, along with all the other riders...

It goes against Blade's ending for why.

You're going off of the fact that the Stone is only counting beings only existing in that one universe. I view it as that the stalemate does exist as along as both Jokers still exist in any universe. The Battle fight starts in a universe, but its participants can go any domension they please and still be counted.