And then as everyone thought it was all over, Yoshika (somehow, in some weird twist in the story), loses her amulet and her full power is released. She teams up with Rumia, releasing HER ribbon and then you'll have to face both Ex-Yoshika and Ex-Rumia as your Extra Stage Bosses...
Or perhaps...
You fight talisman'd Yoshika as midboss of Extra Stage, and when you beat her this time, her talisman falls off. The power overwhelming her at first, she flees(Leading to the second half of Extra stage), and you fight her unrestricted form as the Extra Boss.
THEN, she mentions in her defeat dialogue about someone else with a seal keeping back a lot of their power... Cue new Phantasm Stage, only it'd be unique, not just a sped up, slightly altered Extra. Fight Yoshika one final time as the Ph-Midboss, then run into not Ex-Rumia, but Phantasm-Rumia...
Of course, I'm pretty highly doubting Rumia, or Yoshika as Ex-Boss(Maybe mid, though, unless
, but I think it'd be interesting nonetheless...