Okay time for some guessing. I am sticking by my belief that Cure Beat is going to be Siren. Their styles are too similar and she is clearly undergoing a crisis conscience. The thing is though she isn't Cure Muse, one of the three other girls is more likely than not Ako. And I get the feeling it is going to turn out that she is Otokichi's granddaughter. Who himself is actually from either Major Land or Minor Land.
Even if all of my guessing is false it is still nice to see a mystery.
Haha this kinda remind me of the mystery that they tried to throw aorund when attempting to unveil who Cure Passion was back in Fresh, if it turned out to be that little brat with the glasses it'd be a twist ~ or heck, a bigger twist would be Kanade's little brother XD