[Sorry Zhongli you adopted a goddamn otaku, this is what you get]

It's a classic character type in anime. They're tough on the outside, but soft and gentle on the inside. The "tsun" refers to the tough exterior, while "dere" refers to the more gentle side.

It's most common to see the "tsun" side be portrayed as angry and temperamental, but they can also be cold and aloof.