She's lovely, demure, well-mannered and won't hesitate to throw a grenade at your feet when your back is turned. That's Ryouko for you, the spoiled and mischievous younger sister of Shuutarou Mendou. Arguably the most dangerous woman in Urusei Yatsura, with a persona that often borders on pure evil.

Growing up, always getting her way, having ever luxury a girl could want Ryouko became easily bored. But she found that causing trouble and watching people squirm was the best form of entertainment.

She uses underhanded mischief and devilish practical jokes as a primary source of pleasure. Voodoo dolls, grenades, bombs, guns, booby traps, death masks and that's just a fraction of her tricks. Ryouko often stages large get-togethers inviting many of the UY cast with the underlying purpose of unleashing her some great misfortune upon the unsuspecting fools while she always leaves the party unscathed.

She finds the greatest pleasure in tormenting her brother which is a full time occupation of hers. She knows how overprotective her brother is of her and she likes to use it against him. She'll concoct intricate plots that serve to ultimately infuriate, humiliate or even kill him. She'll even flirt with Ataru just to see her brother fly off the handle.

The manipulative and sadistic Ryouko has a very theatrical way about her. Not only because of the constant theater cliches and props she uses but it's that she's an actress through and through. She keeps putting on this guise of a naive and innocent girl which is incredibly convincing. She certainly appears to be a sweet girl. But underneath this veil of innocence lurks a twisted mastermind. She'll try and harm you, but will act like nothing happened.

Ryouko's servants are legions of faceless veil-wearing kuroko (kabuki stagehands dressed in black from head to toe who by theater standards are officially not there). They execute her every scheme rather comically as if they were in an actual kabuki play. Yet another example of her tendency to be an actress. The kuroko carry her around town in oxcart, a pallanquin or even her horse which is actually a fake wooden horse with two kuroko acting as the legs.

Her main love interest is Tobimaro Mizunokoji, although we're not sure if he feels the same. Most of the time he just tries to get the hell away from her. Tobimaro has gotten his share of pain from Ryouko but he's learned that more than anything, Ryouko is one girl you don't want to make jealous. She'll say that she hold's no grudges as she lands on your face, pushes you off of a cliff, throws a crate of explosives your way and then pretends to weep over your dead body.