yeah @Gustbk , it's a little bit strange, it's not like she was never turned on before... or (because I always try see the consistency in this manga), maybe before she was "heart pounding" like it's often writen, and maybe this time she get a serious and explicit sexual desire... I don't know, but it's clear (to me at least) what she had in mind by wanting to lick the bitter part of Airi. I'm pretty sure Michiru get wet for the first time because of Airi. It's how I understand the "could it be..." part.
I forgot to mention the credit page ! I didn't understood in a first place, but then I thought to one of the last, with "useless lesbian" and finally the credit page really made me laugh. Excellent (as usual). Nice job.