Yuka Kazami is a old youkai. Her life has been long and it has had it's own ups and downs. Japanese through and through, she has had her hand in history a little here or there - She is only one person, able to be in only one place, though she has still had her own influences - Even ones she herself was not aware of. Her history is neither entirely good nor evil - She has saved the world a few times, though her own personal body count is in the thousands for all sorts of reasons.
The flower youkai was not among the people who were at Gensokyo when it was created though she was among the first to actually arrive and take root there in the early years. Her history in Gensokyo up until now had been fairly subtle; While she was among one of the more powerful youkai then she did not put herself in a position where she had a direct influence over things as she does now. Instead she was more of the guardian of sorts - She believed in Gensokyo and what it represented, helping it remain strong against those whom might abuse it or try to cause it's downfall.
Nowadays, however, she does play a bit more of a direct role in Gensokyo's "politics." Her mighty flower field borders the human village - That she tends to protect - and acts of one of the few, if only "safe zones" in the realm on penalty of a short death. Tyrant of the land, she still keeps a fairly hands off and reactionary/defensive influence over Gensokyo.
Yuka Kazami is a very curious woman with many conflicts - She is a paragon of life, yet at the same time she readily snuffs it out if it slights her. She is a terror that (literally) lives off of fear, yet often times is kind and serene. She will crush someone beneath the heel of boot and flirt with the next. Polygamous yet somewhat possessive. Many would call her unquestionably evil yet she overtly does good acts regularly. She is a hero and a villain, saint and a monster. She fears death and yet causes it almost daily.
She is a complex woman, filled with her own vices. Old and growing lazy, she would like nothing more to spend her days relaxing and mutually fawning over a nice blonde woman... With, maybe, the odd bit of excitement now and then.
Yukari Yakumo ~ The two have a romantic relationship with Yuka having quite a bit of affection for Yukari. However, Yuka is quite used to being snubbed by the other for whatever reason - Usually long periods of sleep. As a result, Yuka often finds their relationship regularly soured, though she still cares for Yukari. Yuka is also friendly with the other Yakumo friendly members by relation, though not as strongly as Yukari herself.
Reimu Hakurei ~ Yuka mothers Reimu, even if she didn't have a very active role in the miko's life until recently, past when Reimu really needed one. She offers some show of guidance for her, though in reality Yuka has very little faith in Reimu's ability to defend Gensokyo - Just a figurehead for it. She adores teasing the girl and cares for her quite a bit, though why she does is questionable. Reimu's mother, maybe? Or just as her "guardian" role Yuka plays every now and then.
Parsee Mizuhashi ~ While the flower youkai meet the jealous hashihime only a few times, Yuka found the blonde quite cute and flirted with her. No doubt something will come of that, one day.
Keine Kamishirasawa ~ Yuka has affection for the teacher - Both on a "professional" level as mutual defenders of the village, though she also simply likes Keine. She flirts with the teacher on occasion as well.
Elly ~ Obviously. One day...
Fairies ~ Yuka acts as a mother figure for the fairies of Gensokyo as a whole, though only especially with the fairies that come and live in her flower field - Usually the "flower fairies" as they've come to be known. She gives them a bit of education and otherwise fulfills that Motherly role of caring for them.
Marisa Kirisame ~ Yuka does not hold the same amount of affection, or anything close, for Marisa that she has for Reimu. She has no real feelings either way for the witch - While she stole, and in a way made it her own, Yuka's "Master Spark" that was also a incredibly simple spell. Marisa is probably more positively regarded to Yuka on the basis of her relationship with Reimu, though. Yuka does think, though, that one day Marisa might do something she'd have to kill her for...
Yuyuko Saigyouji ~ Friends by association from Yukari, Yuka doesn't entirely like Yuyuko. Yuyuko is strongly associated with one of the things Yuka fears and hates; Death. On that basis alone their relationship will probably never go very far at all, though additonally Yuka doesn't really enjoy the ghost princess's bubbling personality nor the fact that she takes up a large part of Yukari's time that used to be her own. However, Yuyuko has never really done anything that would cause Yuka to hate her, leaving someone that she doesn't particularly like though nor does she actively dislike.
Satori Komeiji ~ Two times Yuka has met Satori, both times something bad has happened to her flowers. Not only that but Satori is, well, a satori, which Yuka does share the negative public opinion with. While it's not so bad that she won't be civil with her, still, Yuka doesn't really care for Satori. At all. Anything more and she might even get angry with her, too.
Vespa Kumabachi ~ While Yuka is a "paragon of nature", she isn't exactly a fair one. As a flower youkai she, of course, holds bees in a high regard... Which hornets eat. Vespa is a few steps away from getting a parasol jammed into her body, lethally, with her only saving grace being that Yuka acknowledges that it's her nature. She is simply allowing for a certain degree of Darwinism to take hold.
Shikieiki Yamaxanadu ~ One of the very few people still around that Yuka hates. In Yuka's mind the Yama would like nothing more then to get her grubby hands on Yuka to cast her judgement of entirety in darkness, while Yuka would like nothing more to personally drown her into the Sanzu for the same, reversed fate. Yuka has absolutely no respect for the Yama as a whole, especially this one in particular.