As someone pointed out down below, Seto is not dense, but has a terribly low self-steem, so he cant believe a cute girl like Anjou would pay attention to him. That´s why it took for him quite a while to realize that he liked her.
At first I thought it was as always the older women making advances on the guy.
Its nice to see the roles reversed and an actually active guy going to get his girl.
Why so much hate towards both side characters and their story?
I mean... they had quite a good development, which is quite unlikely in this kind of stories that tend to be so "MC-Centric"