@gjj: Subjects are often dropped in Japanese, but "I" is implicit in the original quote. Here, however, with Zuikaku's expression, the intended subject is "You", or Kaga.
Well, following how the previous lines went, I think the last line would be along the romantic meaning of "I wouldn't mind if I die (for you)!"
"I could die happy right now," is probably closer to the sentiment in English. I think she means she couldn't be happier than she is right then, rather than saying she'd die for her.
"I wouldn't mind even if I die!!""The moon sure is beautiful."
See explanation for the pool....yeah?"And the sea is beautiful too."Yeah.What on earth are you blabbering on about since a while ago!?