I don't see how that's possible then because Rachel and Mu-13 are at the bottom of the CS tier list. I don't see how they are unlimited overpowered characters.
What chart are you looking at? Because from what I understand from the Dustloop forums, the authority on BlazBlue, Mu-13 isn't even listed specifically because there's no normal version of Mu-13. If you're talking about Lambda-11 (who plays similarly to Mu-13), then she's smack dab in the middle.
(courtesy of Dustloop)
Mu-12 isn't listed in this chart. If that's who you're referring to, Mu-12 is a different character than Mu-13.
Anyway, you're still not understanding what Unlimited character means. In Continuum Shift (AKA Super BlazBlue)
, there's an Unlimited version of EVERY character. It's not a tier, or rank rating, or anything. It's a separate character (e.g. there's regular Mu-13 and there's Unlimited Mu-13 in Calamity Trigger). By definition, the Unlimited version of a character is godly vs. the regular version of that character. In Calamity Trigger (AKA The Original BlazBlue)
, Unlimited versions of only Ragna, Rachel, and Mu-13 were available along with their regular versions.
Frankly, if Lambda-11 got bumped down, I'm glad. Mu-13 was overpowered in Calamity Trigger.