After some deep and scholarly research I can safely conclude that Kasen indeed wins this dimeless MU
DB will obviously take the most absurd highs for both so Multiversal wank is a given, and in that department Touhou nukes Sonic 20 times over.
There's multiple arguments they could invoke (Gensokyo size wank with Former hell, heaven, and the Netherworld, Otherworld Wank with all the Hells, Dream world Wank, etc) but most of these put the highballs above Fleetway's god Eggman scaling of 2 universes.
The only way DB could throw us a curve ball is if they Rule that Comic sonic= Games sonic (something that's not unreasonable at all apparently)
Their speeds are for the most part equal and since I have no fucking idea what's the difference between infinite speed and unmeasurable speeds I'll assume both are just infinite at their absolute best.

But if they don't rule it with just AP the battle will end up being decided by Hax, and I'm this department Kasen kinda wins but also not really.
Scaling to God Robotnik Sonic should have way better and more variety of abilities, Kasen has lots of counters to most of these but stuff like time travel, imagination manipulation, and evil absorption could end her... That being said Sonic himself never used any of this, Kasen on the other hand has top tier soul Hax strong enough to permanently remove Spirits from the reincarnation cycle and affect reimu herself (who's extremely resistant to Soul manipulation abilities)
DB can still rule in favor of Sonic but haven't he AP difference and how Kasen has few but more reliable hax she uses often (as opposed to Sonic who relies on hax he never used canonically) I think Kasen would win in the end

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