Yukari Yakumo

Yukari is known for being a very youkai-like youkai who sleeps all day and lives for the enjoyment of life. Though she rarely leaves her house, she's well-connected and is acquainted with most of the most powerful youkai as well as anyone having anything to do with the Great Hakurei Barrier or the outside world, although she rarely attacks humans.[4] She has a tendency to toy with her opponents rather than use her full power from the start. If anyone is suited for the role of "mastermind", it's Yukari. She excels at mathematics and is experienced due to her long life.

She possesses superhuman intellect and especially surpasses in dealing with numbers. In Bohemian Archive in Japanese Red, as Ran Yakumo said, this intellect is something that even Ran is not able to understand, to the extent that for example that she is able to determine the depths of the darkness of Avici or determine in an instant how long it would take for Ursa Major to devour the North Star, as it seems. Concretely to what extent this amazing intellect goes is hard to know, but it would be no mistake to think that this intellect far surpasses that of humans.

She often has a great deal of insight and understanding about whatever happens in Gensokyo, and possesses considerable intellectual prowess, as well. Though she seems flaky and unreliable most of the time, when the safety or security of Gensokyo is at stake, she won't hesitate to get involved, even if it means using others to do the work for her. For example, in Scarlet Weather Rhapsody, she treats Tenshi Hinanawi with much hostility after finding out the plot of the Heavens. She could easily be either a villain or a heroine, depending on her whims.

Yukari deals with problems by manipulating others to act to resolve things for her. She seems to rarely act directly except in particularly egregious situations. In all cases, she rarely lets anyone know what her true aims or goals are and sometimes these goals are extremely abstract. Yukari has a well-deserved reputation of being fickle, whimsical and lying often and thus many characters in Gensokyo dislike her. For whatever reason, Yukari takes it all in stride and does not seriously deny any of those comments. She seems to actively try to keep her more obviously-altruistic actions a secret, such as her donations to the Hakurei Shrine in Strange and Bright Nature Deity. She possibly cultivates this image to ensure that people continue to fear her as a youkai, as this is what her true goal for a particularly complex gambit is revealed to be at the end of Cage in Lunatic Runagate.