Fusangshin is a Japanese concept of monster legends. It means that if an artifact is left alone for 100 years, it absorbs the essence of heaven and earth, accumulates resentment, or feels the Buddha's nature and spiritual power, and then gains its soul and turns into a monster.
The Fusang God is also called the Ninety-nine Gods and the Nine-nine Gods. The word "Fusang (つくも)" is traditionally correctly expressed as "Ninety-nine (つくも)"; the meaning of "Ninety-nine" is to symbolize "the long time (ninety-nine years) and "Experiences", "Diverse All Things (Ninety-nine Kinds)", etc.; "Ninety-Nine Gods" are sometimes also expressed as "Ninety-nine Hairs", in which "Fa" also symbolizes a long time and experience, and the concept is similar to the Chinese concept of things becoming fine over time.
PS: I'll leave the article for now, I'll edit it later.