Fujiwara no Mokou is an immortal girl who lives in the Bamboo Forest of the Lost. She was once a normal human but became a person of Hourai and attained immortality after drinking the Hourai Elixir. Her doing so angered Kaguya, and the two rivals have engaged in (entirely pointless) fights to the death ever since.

Even before becoming immortal, Mokou was a skilled ofuda and onmyoudou user. Having now lived for over one thousand years, she has also mastered various youjutsu and acquired a wealth of fighting experience. Her fighting prowess is such that she can easily dispose of most youkai.

Those who have consumed the Hourai Elixir are referred to as a "person of Hourai." The elixir binds their existence to their soul rendering them immortal, while also giving them the ability to create new flesh at will should they require it. Their immortal soul ensures their body will not age or suffer at the hands of disease, but it can still be wounded and pain can still be felt.

The phoenix―a legendary immortal bird of fire that, if killed, rises anew from the ashes. Perhaps no word is better fit to describe Mokou's fighting style, what with her youjutsu abilities and immortal soul.

Veiling herself in wreathes of flame, her burning will crashes into the one who opposes her. What sets her heart ablaze? Hatred for her old rival? Or the joy of feeling alive once more, if but for just a moment? The look on her face suggests she abandoned such ponderings long ago.