I don't know what to feel about this. I found Miyako a bit forceful. Swap her with a guy and there you have rape.
But the magic of yuri makes it ok I suppose.
Okay, reading your comment, I had to re-read the manga to figure out what you might have been referring to.
And yes, Umi has some protestations, but they are not from a lack of desire to proceed. Her first hesistancy is in pages 8-9 where she is struggling to fully understand and believe that her affection is indeed reciprocated and that she is not just being pranked. Her next objection on pages 11-12 is that they have to stop, not because she is finding the experience unwelcome, but because the kids might hear. Once a token amount of noise mitigation is put into place, the act is once again given a green light. The last possible piece of contention is on pages 14-15 regarding whether Umi is in pain and not enjoying it or not. At the first sign off distress, Miyako stops cold and asks for a status report. Umi admits in her head that it hurts "a little"--but this is pretty clearly due to haste and inexperience on both girls' parts, and not because anyone is forcing anyone to do anything they want. Umi's narration balloon, in fact, states plainly "I don't want it to stop" and she also vocalizes "Please don't stop".
So we have one clarification of validity, one objection due to noise which is addressed, and one instance of discomfort that is judged an inadequate reason to halt the action, due to the net positivity of the experience as a whole. Awkward and fumbling? Yes. Rapey? I'm not seeing it.
