Note that giving lessons on blocking while inside of a mall might not be the best idea either.
You will be going to a high school as well, remember that. In fact, since Rainer is 17, Gekkoukan Gakuen should be his school (unless you want to have him go somewhere else?).
And maybe Sasha's as well (unless you want her to be in college)
In fact, for just a sort of special affect. Today is Saturday (but I think some schools like private schools have half days on Saturday). So we will say that (for those in high school) school ended not too long ago.
And since that is the case, if you all want to meet the other Gamer before they leave school (cause it could be anyone from a teacher to another student) then you should hurry.
I mean, if you guys seriously want to go off to some place to grind skills, then be my guest.
Just remember though that you guys don't really know much about your own power or how it works exactly, so grinding could be somewhat difficult. Going to go see the other Gamer could teach you more about it.