Basically, Maria is being so pure and cute.
Kanami doesn't want to disappoint her.
And Lastiara just enjoys the chaos.
But these two are seriously down bad. Kanami should throw away his cool big brother act and just say that Maria is a burden. Even though it's gonna hurt her. He is also too arrogant that he thinks he can protect her anytime in a place full of monsters.
And Lastiara should slap Kanami in the face for bringing a child to the most dangerous place in the world. She is not laughing because Kanami fooling himself is funny. But because it looks like the book she loves where the characters have a lot of emotional conflict.