Touhou Project has a considerably loose canon which allows fans to interpret the characters however they wish. Well, here's my head canon for aged youkai called Yuuka Kazami.
• Her birth was years ago, at least several millenniums; definitely a good time before Gensokyo was created and even before Yukari Yakumo came into existence. Her view on humans was shaped because of this. Youkai and Humans were constantly in conflict during those times so of course she was dragged in. She wasn't even that old when humans attacked and failed to kill her... then again, her precious flower parasol gave her a second chance at life since she constantly cared and spoke to it. Only right she slaughtered the humans that tried to kill her.
• When Youkai are born, it's said they rarely travel together. For Yuuka, oh so very true. She definitely picks her company, but she does seem to enjoy solitude more.
• She's the embodiment of flowers En Massé. Flowers don't move very fast and this reflects in her speed, but like all plants abilities to hold even the heaviest things together (such as earth), her physical prowess is something to try matching.
• To manifest flowers where she wants, it's a very metaphysical break down of surroundings, manipulating molecules and forcing them to be something else. It's very complicated, but she's had practice long enough that it's just simple hand wave or gesture.
• Yuuka had a relationship. It was still before Gensokyo so she was fairly young and during her travels to various flower fields, a sunflower field specifically this time. Her very human appearance often causes confusion, but it was the first time it attracted a male to coming back. The youkai and human conflict was still going on so it's understandable she was surprised. When the humans found out, the field was burned and his corpse fed to the flames. Yuuka put the fire out, but the injuries were too much. She fed his remains to her parasol and she murdered the humans with her bare hands and ate them. Before moving on, she regrew the sunflower field and left it as a memory.
• She's usually a chronic liar for the sake of teasing, pestering, trolling, etc.
• Yuuka's powers diminished while she slept in Mugenkan, but now that she's been awakened, they're back and getting stronger. She probably uses a 1/4th of her strength on a good day. She did make Elly before falling asleep as well as contract a Vampire and trap Orange in the realm with her (then again, Orange was always a stumbler. There was no effort there).
Still being worked on and hammered so come back later~♥