I think Sagume said something along the lines of 'This game is quite easy' during development and hence the difficulty went boom-bam XD
As for the permission from A-One, the tracks used are from Odyssey Eurobeats/Jessa Stebbins. I don't know if the copyright holder is A-One or if it is Odyssey.
It seemed like there is a big gray area when it comes to using toho music for fan games. Some elaborate reddit discussion scourging later, it seemed as if it was alright to use the music with credits to the original creator (done on the game entry page). It might not be okay (in which case, we don't mind removing the audio tracks). And similarly, we also opted out of the audio design category for the jam.
Hope that explains it!