In the world of Inuyasha, demons were actually living creatures too; their methods of coming into being and reproducing simply differed from those of ordinary creatures in nature.
Demons fell roughly into three types:
[The first type] were natural-born demons.
How exactly they first came into being was no longer known, but after hundreds or thousands of years of reproduction and inheritance, many had formed tribal societies, and some even possessed powerful forces that ruled entire regions. Examples included the Dog Demon Tribe represented by Sesshomaru, the Panther Cat Tribe, the Demon Wolf Tribe represented by Kōga, the Thunder Beast Tribe represented by the brothers Hiten and Manten, and the Hundred Demons Bat Tribe represented by Ōgamaru and Tsukuyomaru.
These could be regarded as animals that gained spiritual awareness and became demons capable of taking human form.
Their lineages stretched far back, and each had its own accumulated resources and heritage.
Corresponding to the animals were demons transformed from trees that gained sentience, such as the Great Katsura Tree, the Tree of Ages (the Sacred Tree), Old Man Bonsai, the Life-Melting Tree, and the Human-Faced Fruit Tree.
[The second type] arose from the corruption of living creatures.
The most typical example among them was Peach Fruit Man.
He had originally been human, but out of greed, he practiced immortal arts, then killed his master, the Peach Immortal, and fed villagers to the Human-Faced Fruit Tree to produce Human-Faced Fruit, which he used to refine an elixir of immortality. That alone would not have made him a demon, but after eating the Human-Faced Fruit and borrowing the demon power of a Shikon Shard to remodel his flesh, he became one.
Dao Qiu, the swordsmith who forged the top-tier demon sword Soul Seizer, also counted. (Ogre Seizer sounded bad, so it was