Quite frustrating how people really can't give any credit to Seto. I'm pretty sure his line meant he's realized that he likes her more than just a casual crush at this point.
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.
Bruh, is he being serious with that realization comment? Had to read 3 times before I realize that what was written is what he meant and feel.
Its more obvious that he actually really liked her from way back but what's not still fully confirmed is Anjou being playful is only mere playfulness or the feeling towards each other 100% mutual. @TuragaBimey nice of you to see it that way. I can see why you think that's what he meant but still it doesn't change the fact that it took him this long to come to that conclusion. Many of us thought this was already pass that point.