There are countless tiny "spirit seeds" in the world - an ancient existence between energy and consciousness.
They cannot survive independently and must be parasitic in a living body and absorb the host's emotions, experiences, and obsessions to grow.
When the host is not strong enough or if the spiritual seed is mature, it will swallow its soul and inherit some of the host's characteristics and memories. Every life is a "container of spiritual seed" and is called a "shell".
It is also possible for a spiritual seed to coexist with its host. The stronger the host and the more intense its emotions, the faster the spiritual seed will grow; however, after the spiritual seed matures, there is a certain chance that it will backfire on the host.
There are "spiritual cultivators" in the world: professions that can sense, guide and even trade spiritual seeds, and control the "life cycle" of the powerful.
