Brother is too used to have everything come easy. As soon as there could be pushback or any danger, he falter. :X
Also, yeah, that’s a mixer, not a “blind date”. A blind date is a normal 1:1 date with a person you have never met before, usually introduced by a friend.
A mixer is a group activity with a bunch of people, usually mostly composed of single people. Because a big number of people interacting is necessary to build the mood, there CAN be couples participating to fill up these numbers, and they often came with bonus injection of a bit of “premade“ romantic mood, but they should be openly known, and both should be there. But of course, in manga/anime, they are always secret, to add drama… xD