There will be happier entries, these were already in editing before I did the Shaman King run.

Tenjo Tenge is the ultra mature martial arts anime very much adult in nature, Maya who is first introduced in a small body to preserve her chi only to reveal a very sexy body in episode 1, stands out as the current head of the school's Juken Club.
She hires Nagi and Bob after a quick scuffle mostly because Nagi falls in love with Maya despite Aya pining for the delinquent.
But after the bowling alley incident, Maya decides to taunt her sister about the whole situation between her and Nagi leading to a fight between the sisters.
The fight ending with Maya threatening to kill Aya with the very sword that killed off their brother in Tenjo Tenge's more convoluted back story.
Maya didn't need to ruin her own sister, the whole situation could've been handled better but Maya just makes herself look needlessly cruel for no reason and while Aya is not entirely innocent, she didn't deserve to be humiliated.