Yeah - this really reminded me of Ice Princess, and I agree. There's something charmingly gentle and innocent about this sort of set-up. It's as if the romance is almost secondary - they grow together and form bonds as people, and then that sort of morphs into romance.
And the younger siblings are central to all of that - not only do they provide a reason for the mains to spend time together - they generally pick up on the growing romance before the mains do, and then encourage it.
Am I the only one who thinks that Steins;Gate is overrated?
Maybe it's because I grew up reading science fiction and it's always been my favorite genre, and time travel one of my favorite sub-genres, but I just found it to be sort of shallow and tedious. That and something that is unfortunately all too common in anime, unnecessarily bogged down with an intensely irritating MMC. I'll give it credit for an interesting climax, but to me, it was too little too late.