Outwardly, Yuyuko is cheerful to a fault and always optimistic (though not to a point of stupidity). She enjoys talking to people and sticking her nose in places it doesn't belong, and welcomes everyone with open arms and an open heart. She likes humans by default, and if any in her watch find themselves in trouble, she will make sure that they end up safe and back in their rightful place. She treats her bodyguard, Youmu, more like a dear family member or treasured companion than a servant, which is indicative of her general way of forming bonds -- it doesn't take a whole to get her to like someone and latch onto them.

However, her sunny side isn't without its downfalls, that being she's a bit of an airhead. Yuyuko has an infamous love for food and anything relating to it; she won't hesitate to steer conversations into the realm of food, and is said to always have a food-related quip on hand. Her attention span is limited at best, her mind constantly wandering astray from relevant topics. She's easily distracted to a ridiculous level, following and fixating on anything that catches her fancy--such as when she tries to resurrect her own corpse because she wondered whose corpse it was in the first place, belying the whole can of worms that opened up. At worst, she once forgot what she had for breakfast that morning, and put her focus on trying to eat a sentient night sparrow character because she "looked tasty." "What does this button do?" seems to be a question she asks often, or forgets to ask in preference of pushing the mystery button first and asking questions later.

But Yuyuko is undeniably an actress -- it's subject to debate how much of her outward personality is just that, an act. It's heavily suggested that her airheadedness is all a carefully-constructed ruse for the sake of entertainment, and at the very least, she does play dumb at convenient times. In reality, she's proven herself time and time again to actually be incredibly intelligent, and perceptive to a frightening degree. Yuyuko is cunning and a very good manipulator, managing to out-gambit both her closest friend, Yukari, and a great deal of the Lunarians, as proven when she managed to interfere in a carefully-planned trip to the moon that was already being pseudo-sabotaged by two different parties. It resulted in her waltzing into the moon's capitol in broad daylight (relatively speaking), allowing her to steal things from their treasury...even though all she took in the end was a thousand-year-old bottle of sake, which brings us to: Yuyuko often does things or makes comments to rile people up or make them uncomfortable, as getting reactions is a source of amusement for her. She teases Youmu on a regular basis and is often intentionally vague when people ask her questions just to see them get irritated. In that case, Yukari expected her to make off with expensive treasures or legendary weapons, yet all she presented was a bottle of alcohol. Yukari is oft-touted as the series' master manipulator, yet even she can't always read Yuyuko or predict her movements. 

Otherwise, Yuyuko is what you'd expect from the daughter of a nobleman, and the last remaining head of the Saigyouji family. She's a bit spoiled, and as such can come off as lazy and flighty when she expects people to do things for her or pick up after her, and she can be a tad bit entitled. She's also a voracious reader, probably contributing to her intelligence. Fitting her position, she is charming, ladylike, and cultured. Although Youmu is supposed to be her swordsmanship instructor, she often forgoes lessons because she finds swordfighting 'unrefined,' and doesn't feel like wasting her time with it. Yuyuko takes her position as the head of the Netherworld (and really, all grave, serious situations) as no joking matter, dropping all presets of being an incompetent, bumbling ditz. Despite her overall eccentricity, she was given her position of power for a reason. It's difficult to make her truly angry, and she finds it hard to hold grudges, even with wrongdoings against herself....though when she does get mad, it's said she's terrifying.

But such a summary is incomplete without mentioning Yuyuko's life as a human. Back then, she was an anxiety-ridden girl suffering from severe depression and lack of self-worth due to the fear of her powers. Canon doesn't make it clear whether or not her powers would go off at random, or if it was an isolated incident or two, but either way it is what instilled most of Yuyuko's morals into her. As such she values the lives of the innocent, particularly humans, to big degrees. As she became amnesiac after she died, she was something of a blank slate and her personality changed accordingly. Having forgotten the toll her powers took on her and those around her and essentially coming into the world as a supernatural being from the very start, she viewed her powers trivially, calling them 'fun' and flippantly disregarding the heroines' pleas for her to stop her insane corpse-resurrecting plot. She was more arrogant and foolhardy, and it wasn't until she regained her sorrowful human memories that she also regained a large amount of her humility and kindness.