Yuuka Kazami is a youkai (term used in japanese to describe supernatural creatures) who resides in Gensokyo and to be exact in a Garden of the Sun (basically a LARGE sunflower field).
Yuuka loves flowers, especially sunflowers, which goes along her ability to manipulate them in any way she likes (pretty cool huh?).
She may look young, but actually is over 80 which explains her wide knowledge and power level. Many people are afraid of her but she is in fact pretty polite and peaceful also pretty dormant and doesn't care about some stuff at all (unless flowers).
Yuka is actually pretty powerful (one of the strongest in Touhou universe), although pretty chill she becomes merciless and tends to look down and toy with those who disturb her despite being weaker than herself. Her power of manipulating flowers may seem like a small thing but is actually a manifestation of the power of nature inside her by itself and does not in fact limit only to flowers. She can make plants grow, bloom, and do the other cool and funny stuff, for example she can impale her foe on a overgrown rose thorns, or feed you to a venus fly trap.
Overall, pretty cool 10/10 would hang out with