People are already forgetting that we're almost 20 chapters away from the true End. Given how condensed this chapters are, it may feel quite long; but it is not bad enough as how some series artificially extends themselves.
At this point i think Fuutaro doesn't even care who rena is, he is focused on the present and piss off that Itsuki and Ichika are trying to use Rena as a bust to their position instaead of approach him directly. And because of the it and Ichikas precedent he is midly angry to be lied, but...