User blog comment:Monkey.D.Me/RAGE ON!! Part 3 (〜￣▽￣)〜/@comment-109.228.146.154-20120527023836

"W-why you, Luffy... You got me blushing!"

I'm pretty sure that was Franky (Nami) saying that, doesn't sound like something Robin would most likely say (though I wouldn't mind of course if she did say that).

Anyway, my bets on the Yonko is either BM or Kaido (the reasons for the latter are the same as as Zori9).