Mitsuki, As Sung By...?

There are a few episodes where singing it a part of the plot. Most notably, both of thr "Karaoke Episodes" and the one where Mitsuki replaces her father in the theatre circuit.

Does anyone, who WON'T say some unhelpful criticism of the show, know who is the real singer for Mitsuki? Her voice is actually very lovely, whoever she is; range, depth, and emotion are very present - it's a strangely powerful element in only a couple of episodes of this unique and rather unpopular series.

Thanks in advance for any HELPFUL answers.