Hayama is a very calm, passive individual. Sana does not like this. And all hell breaks loose. As time passes, we dive into the characters minds and home lives. Relationships develop and deteriorate.
More opposition occurs as new characters are introduced.
Most of the time. And although the show will sometimes shift focus slightly to put another character into the spotlight, the main attention is always aimed at the dichotomous pair of Sana Kurata and Akito Hayama. There are several crucial serious, dramatic moments that are handled quite brilliantly in the show. And as the plot goes on, and as the antics and the angst continue, we become more and more attached to the characters, and one begins to notice that some of the things they do might seem like they're done for a laugh, but if you probe deeper, you'll find that certain actions of a given character are actually windows that give a view of the emotions of that character. Sana likes to sing.