Azwan.

It is entirely possible to go down ranks when using any Circulator (unless you have bought a Cash Shop Inner Ability Lock, which by the way only exists for B and A ranks, lol). Well except for the S Rank Circulator that they gave out in a Hot Time, that instantly brought your Inner Ability to S Rank.

Speaking of which, if you do get that, I highly suggest getting all three lines before using it because it will make all of them S Rank iirc. And don't reset them, they'll most likely go back to C Rank.

They gave out TWO of those, remember?

And according to cullen and one other person, the S-rank one didn't work for people with >1 line. Not 100% sure, though.