Mona De L'Orange is a character from the anime Let's Go Quintuplets!. She first appears in the episode, Krystal's Best Friend. Her father is the owner of the Jolly Joker Juice Company.
When she was in kindergarten, her best friend, Krystal Miller accidentally caused her to spill juice on her costume, (wet herself in the Japanese version) forcing her to wear her brother's old clothes.
She then spends much of her time trying to trick Krystal into embarrassing situations as revenge for what happened, but she is invariably unsuccessful.
Though friendly to all except Krystal, she is somewhat the antagonist of the latter half of the series, though she is more of a vengeful brat rather than a credible villain.