Childhood
Living under the shadow of her father and her enormous family, there was a lot of weight on all Kuromura's shoulders. Though they have no KG or Hiden, the clan have been around for many generations, and solidified themselves in the village as a helping Clan and assisted so much they earned a Compound area, off to the East. In the Third War her father, Arashi, became well known for his wind & water jutsus (unable to combine them, but he was formidable all the same). She barely scraped through the Third War herself as a genin, troubled by the bloodshed and fighting.
Adolescence
The Chunin exams is what changed Junai for the worse - and he began a slippery slope of craving power and stability that he thought the village could not give him. Kotori herself earned her first deep scarring on her upper chest from an overzealous Suna Genin, and still has the twisted scarring to this day. She becomes a Jonin at 20 with little fanfare.
Adulthood
Her brother defects when they are 21. For a short time she becomes obsessed with finding him, which leads to Hiruzen giving her Team 2 as a distraction: she isn't used to the backtalk at first, and it takes a lot of getting used to for them all. Unfortunately on a mission that proved too difficult, Kotori lost her team to missing-nin at 23. From that point it was a slope of anguish, and she became unpredictable and a danger to herself: going into frenzies when she thinks she hears anything to do with Junai. Going off-mission to hunt him down was amongst the many things that broke the straw on the camel's back, and a trial was conducted. The Hokage and his advisors, after listening to statements from her family and friends and coworkers, opted to remove her jonin status to help her recover from her team's death.
She temporarily moved to Getsugakure as a civilian, taking on secret merc jobs on the side and honing her ninjutsu and skills. Just prior to Part I she returned to Konoha, before disappearing again but leaving no trace this time: sometimes there would be hints of her return (perfume in the academy hallways, strands of salmon hair in her childhood bedroom, watchful eyes at night). Eventually it became clear she was honing her skill as a shinobi, and she returned between Part I and II with her new set of skills. Deemed fit to fight and protect her village, she was reinstated after a series of unique tests.
Part II has a Junai arc, in which he does attack Konoha, however Kotori and Naruto defeat him together.