[wao]

I'd think the katakana usage was used for emphasis, not to mean another word entirely, actually...

That would make the large words "Thank you ve~ry much! ... And exactly what is so good about that book, I wonder?"

At the bottom it says "Yasaka Kou" and "Nagamori Yamato", presumably the authors, and then "Yamatooo... You don't say those things here in such a loud voice!
It's your fault for yelling even though you knew I'd say it, Kou.
But why don't you understand the greatness of ●● doing △△ to ××!!
...Kou, that is precisely the kind of thing you don't say in a loud voice."


I think that roughly says it.