Fighting is often seen as violent and aggressive, but Kiyoshi doesn’t reflect this. He is quiet, the strong silent type. He keeps his distance from people, and chooses to not intervene most times. He is tough when you upset him, often getting violent and upset. He will do anything to protect those he cares about. 

Kiyoshi has a medium to medium low voice, that does not need to show much emotion. 

Voice reference 1 (aizawa): https://www.youtube.com/watch?v=QyDKtdnhoM0&t=203s