If her bestie, Plu, is described as a big smug meanie, then Tetra is a straight-up bully.
Tetra is a girl you absolutely do not want to bump into.
She is hateful towards everyone and so ruthlessly harsh that some consider death to be a preferable fate.
Thankfully, she is quite dull, so it's not too difficult to outsmart and flee from her.
Just hope that you don't run into her again afterward...