Sea Breeze

Same. I'm happy with this turn of events.

Just waiting for the man with the guts to say that in front of him

You are our Guile.

Umi's remark (page 11, panel 2) is not meant to imply any sort of incestuous
behavior between Umi and her father. In Japan, the whole family, mom, dad
& the kids, traditionally bathes together (until the kids outgrow the practice).
Plus, Umi and her dad, being carefree islanders, probably go skinny-dipping
together once in a while (along with mom). On page 16, bottom left, Umi was
about to step out and casually greet her father, so she's used to being seen
naked. Her family clearly takes a relaxed approach to nudity.

For all those reasons, Umi has probably seen her dad's penis many times,
but never erect, which is why the MC's boner looks "so different."

Note that the MC himself isn't the least bit perturbed by Umi's remark,
so he obviously takes it for granted that Umi has seen her dad naked,
for the same reasons I have outlined.