I always thought Satoru had more of a "lead guy" vibe than Shun (as I wrote elsewhere, Shun has this "like me while you can because something horrible is going to happen to me and then I'm going to die" vibe going on), so I wasn't surprised by him in the recent episodes. He seems like the sort of character who may make mistakes and stupid things, but in the end does the right thing.
I don't think he was ever a comic relief... it's just that they're all very young kids. Shun is more mature than the rest which obviously makes him stand out, while Satoru is a 12 year old boy, and behaves like one, which includes pulling Saki's proverbial pigtails because that's what many 12 year old boys do with the girls that they like.
I'm sure he's going to mature at least a bit after the timeskip, and I can see him and Saki eventually ending up in a relationship of sorts. (I don't think it would be NTR... Saki may have a crush on Shun and vice versa, but it's not like the two are boyfriend and girlfriend, and in any case they're twelve. Their feelings may change.)