Nanoka is a modern girl who suffered a tragic accident on September 1, 2011. While riding with her parents to check on her grandfather who had been admitted to the hospital a huge explosion engulfed her parents car which then cratered into the blast hole killing them both. Nanoka was blown free of the car and awoke in a firey landscape staring down a creature with a decapitated head in its mouth. Stunned she turned to flee only to be attacked from behind. Her next memory is waking up in the hospital with her grandfather and learning of her parents passing.
From that day forward Nanoka was raised by her grandfather and his new live-in maid, Fune Uozumi. Told that she was a weak, sickly child she was made to drink a pungent green beverage and told that it was to fortify what little strength she had remaining. Eight years later Nanoka becomes curious about the strange explosion and sink hole that claimed her parents lives and begins to research the event. Returning to the scene of the accident she passes through a gate and the shopping street that stretched out before her is replaced by a bustling duplicate from the 1920s. Soon Nanoka meets Mao and discovers that the explosion that killed her parents was a side effect of a battle between Mao and Byoki during the Great Kanto Earthquake, the severity of which stretched through the time portal and struck her family's car.
Nanoka soon learns that during the accident she was swept into the past and like Mao she too was cursed by Byoki. She carries with her the demon's blood and the green drink she has been imbibing since childhood was not to keep her healthy but to rob her of her demonic powers so as not to draw the attention of Byoki who now lives in the modern age and continues to seek out the girl in hopes of joining with her to regain his own powers.
The Meaning Behind the Name - 黄葉菜花
"Kiba" (黄葉) is a fairly common Japanese surname. It also means "autumn colors" and can reference the turning red of leaves during fall. "Nanoka" (菜花) is also a common girl's name in Japanese. The kanji used to write it are "vegetable" (菜) and "flower" (花), though together they refer to a specific type of plant, the "rapeseed".
Though Rumiko Takahashi has not said so, it is possible that this plant was in the collective consciousness in Japan at the time due to a great number of rapeseed that was being planted in the Fukushima area to help absorb radiation in the soil following the nuclear power plant's meltdown in the aftermath of the 2011 Tohoku earthquake and tsunami.