Man, Yuuichi is so pathetic it's a little painful to watch. I don't know what these two girls (formerly including Sei) see in this guy, Tsukasa is so much more of a boyfriend material than the alleged protagonist is and that now makes Sei the luckiest girl of them all with him around for her.
Achievement unlocked: Double date?
Sei was going to deny it, but by Tsukasa's sheer confidence and willpower she relented.
Now it is a date.
Achievement unlocked: First date!
But asking her about other boys she's liked is just asking for trouble. It's a bad move in much the same way as her asking him about other girls he's liked... that was a flub no matter how I see it. Never talk about other girls when on a date with a girl you like, and vice versa; so he shot himself in the foot with that move. It's far from over though, I just hope he doesn't flub everything on this first date.