I agree. Takumi's presence changes the feel of the series considerably. If he wasn't there, I don't think the series would stand out at all. He has a reasonable attitude, acts responsibly and thoughtfully (not intending to pry into Nozomi's past until she brought it up), and acts calmly in most situations. He comes off as very casual and adult, perhaps owing to the circumstances in which he was given a name and a family. Strangely enough, in the flashbacks with Fumino, he displayed the same sort of attitude then that he does now. He would help her get back up when she felt down, in a manner in which she could help herself rather than rely on him.

Any other character would protest or overreact to Fumino's brash demeanor, but he treats her tenderly, knowing she is just using it as a defense mechanism. That only makes her worse, but I got the impression that he already knew that she had some kind of feelings for him.

I took the scene where she confessed in that he was less surprised that she liked him, and more surprised that she was so honest and upfront about it for once...at least until the scene after the credits ruined that bit of speculation. He was pretty flustered about bringing it up again, and Fumino deflected it rather casually. A pity.