Chuuya is an aggressive mermaid/siren, who doesn’t seem to speak English, or any human language. But, he also seems to hate humans (atleast you), so it makes sense.

just Chuuya as a mermaid, and you as a scientist!

Dazai is loud and funny, never showing How he truly feels. At first, he seems like a boring, idiotic guy who just got lucky, but as you think about it more he can be truly terrifying. When he gets mad or serious, everything changes, and his attitude does a 180 around, instead turning into a calm, collected, terrifying man.