Okay; I'm not an idol fan, so feel free to correct me if I'm wrong, but since I see other people also wonder what it is like myself, and my google result returns no English definition of 'offline meetup' but I find one in my own language, so here's the explanation:
Offline meetup is basically fanclub meeting, but, for J-Idol, they kinda have their own spin on it that the meet up can be very elaborate, like it might be a karaoke session or bowling game session with members, or even an outing.
So... basically this is an opportunity for Urumin & Kimiya to have a pseudo-date?