tl;dr: A story with really solid character development built upon really solid, and adorable, relationship development built upon a surprisingly solid plot. 

This was much more interesting than I thought. Based on the description, I expected it to be mostly lighthearted fluff without that much intensity, focused primarily on just being cute and sweet. While the core relationship certainly does produce a very strong stream of cute and sweet moments, there's a lot more to than just that though. The characters have a really good amount of depth, with backgrounds that greatly impact them and personalities with flaws, both of which play a major part in the character development they go through. The two main characters are great in this regard, with Tamahiko especially showing a lot of growth slowly and steadily from someone selfish, without ability, and without hope to someone looking optimistically towards the future, working his hardest, and caring about others. This development is largely the result of the relationship development between him and Yuzuki, which is also done really well, also being slow and steady, but constantly growing in a way that makes it feel really well paced. Part of what helps is that contrary to my expectations, there is a good amount of plot that drives this relationship development, and though it never gets really intense, there are a good amount of parts with suspense and some darker aspects to balance out the more lighthearted fluff and add more layers to the relationship between the two. Furthermore, it wasn't just the two core characters, but a number of side characters were well developed as well, with Tamako and Ryo especially having solid development and good stories in their own right, though their interactions and relationships with the main characters was what truly makes them such great characters. And on top of that, it ends quite well, having solid conclusions to the various character arcs, with the part contrasting Tamahiko with his father working especially well, and also having a very solid ending overall for their relationship arc, where everything ends in a truly happy way that feels fully believable and something that the characters deserve to obtain and you feel happy for them doing so. The art is also pretty good and quite adorable at times.