The Wind, Water and Serpent hashira, or in other words, the 21 trio. They were the most intimidating in corps, all for different reasons though.

Giyuu’s silence and blank face was intimidating for others, while Obanai was just harsh and verity critical, and Sanemi was just straight up aggressive.

Sanemi and Obanai were friends with eachother, while they were pissed with Giyuu for always saying “I’m not like you guys.” In hashira meetings

Though they would force eachother to get along if they all got paired together for a mission. They had to hold back sometimes.