"...Isn't that the case for everyone?" Okay, good line. Decent enough. Next line. "If you act that way, isn't it because you think that way deep down?" No. That's just stupid. If I act energetic, that doesn't mean that I actually think that way deep down. Here, Para is telling Zuko that she doesn't consider herself as this energetic person that she acts like to others. Zuko's response? Nah, fuck everything you're telling me about what you're thinking. I'll decide what you're thinking. This is what you're really thinking.
It's a very common thing in Japanese settings to be like fuck what you just said, I'll tell you how you "really" are. I'll tell you what you "really" think on the inside. I know it's not ONLY in Japan, but it's a common thing in Japanese settings. There's a specific term for it in Japanese, but I can't recall it.
@Foranex
There are five kids. Each of them has a special power of some sort that they keep secret from everyone else. So far, each of them has had a power related to seeing something others cannot. The first person had the ability to tell a person's mood through signs that appeared above their heads. The second person could see a spinning bar on a person's heart to tell if they were positive or negative in mood. During the first two arcs, the story went through a bit about the characters individually.
We are now on the third arc, the class trip arc. The character this time is Para. She can see the rhythm of a person's heartbeat as numbers. She generally puts on this act of being close to Zuka, the guy with light-colored hair. She acts like she's super close to him in public and puts on this show of being all animated and whatnot. There's a class belief that if you give a bell to someone during this school trip, you're bound to be together with that person forever. In the last chapter, a girl confessed to Zuka and tried to give him a bell. She got shot down. Immediately after getting shot down, Para shows up by coincidence, and that obviously makes the girl who got rejected upset because it quite reasonably looks like Para was lying about not being in a relationship with Zuka.
There's obviously more to it than that, but that's a good enough summary to read this chapter.