Belial

Belial can't talk because he lost his voice to an angel when he was young.

Jjyu, the devil hanging onto his horn, was born as the smallest devil and was considered to be useless. After he found out that he could read the minds of other devils thanks to Belial, he speaks Belial's mind for him.

However, Jjyu is foul-mouthed and has a habit of adding his thoughts after conveying Belial's mind. So when you talk to Belial, you can hear Belial's kind words and Jjyu's foul word