Yuuka is a rather powerful and dangerous flower-loving Youkai. In Lotus Land Story, Reimu and Marisa break into her mansion in the dream world of Mugenkan, and she defends herself. In Phantasmagoria of Flower View, she goes out to enjoy herself, trying to remember why the event that touches off the game's story seems familiar.
The "Flower Master of the Four Seasons".
Final Boss of Touhou's Lotus Land Story and later a recurring playable character, as well the the fourth PC-98 generation character after Hakurei Reimu, Kirisame Marisa and Alice Margatroid to reappar in the Windows generation (specifically in Phantasmagoria of Flower View).
A highly dangerous youkai with the power to manipulate flowers and reputed creator and original wielder of the Master Spark (which Marisa later "borrowed"). Hinted by Hieda no Akyuu to exhibit a rather polite facade, provided she or her flowers are not harmed. Rumored to be incredibly old from her dialog with Shikieiki Yamaxanadu. Once described by ZUN as "Youkai moe~". This might be meant as a pun, given that the literal meaning of moe is "budding" and Yuuka controls flowers.