Overview
Tsunshun is a little different than Tsundere, instead of displaying an attitude of tsun (hostile) followed with a dere (shy, vulnerable). This character first display a hostile attitude followed by "shun..."(a Japanese sound effect meaning melancholy, down, sad, depressed, etc).
Apparently, this term is coined by Nobara Yukinokouji, which is considered to be a new form of moe.
While Ririchiyo Shirakiin thought of fixing that bad habit of hers, it seems that the journey ahead is not going to be a smooth ride.
Ririchiyo first display an example of how Tsunshun could be : insulting (mostly acting tough) her friend with extremely mean words, but later wrote a long but proper apology letter to that same friend, seeking for forgiveness. Though the same thing happened later on, this usually means she refuse to properly reflect her own mistakes, although she promised not to repeat it again.
While those who understand that personality, or feeling would think she's a cute person. Others may not think so, and would misunderstood her well being entirely. This may require a proper study in the Tsunshun field : How to handle such person with a tsunshun attitude, and so on.
Anyway, this archetype somehow does not create a negative impression on her SS, Soushi Miketsukami.