Source: Siren Maniacs, page 40-41
Siren 2: Creatures, Part 1
Mother
母胎
Long ago, the Ancestors (a group of intelligent beings) fled to the World of Nothingness to survive after being chased by the light, losing their forms after a time close to eternity had passed, finally merging into one consciousness. 44 years ago, due to the effects of Yamijima's development, a "phantom" of the real world Yamijima appeared in the World of Nothingness, and Mother began to stir from her long sleep. 33 years ago, a small rift created between the real world and World of Nothingness allowed a drowned body (Shu Mikami's mother Yayoi) to wash through; her image was copied by Mother, allowing her to give herself a form. And then, 29 years ago, Mother birthed an Offshoot (dove) of herself possessing a temporary body to search for a means to evade the effects of the light, wishing to return to the Earth's surface, sending it to assess the situation in the real world. After releasing several doves, Mother confirmed that she could return to the surface using a human shell, and began efforts to reclaim it.
Since Mother is made up of the Yamirei, an intelligent body made of pure energy, she is able to use many supernatural abilities such as creating things from nothing and dragging people to the Reflected World from the real one. As viewed by humanity, these could be seen as the actions of an egotistical god.
Yamirei
闇霊
As strange beings born from the awakened Mother as though splitting off from her body, they are the former controllers of earth who have lost their form. They attempt to avoid the light by wrapping black cloth around themselves, but are extremely sensitive to the light, and simply by staying too long under streetlights or lamps they begin to steam, finally vanishing. They appear to have physical bodies, but they can suddenly teleport, and their bodies swell to several times their normal size when they take damage, so it is apparent that their bodies are constructed in a completely different way to that of human beings. Upon entering the corpse (shell) of a human they alter its insides and transform them into a Yamibito.
Offshoot (Dove)
分裂体〈鳩〉
Those known as "doves" in the game are "offshoots of Mother" released into the real world to survey it. Their goal is to descend to the Underworld with a human (of either gender) and have them merge with Mother. Four doves are known in the game from 29 years ago (Offshoot A: Kanae), 19 years ago (Offshoots B and B'), and the present day (Offshoot C: Yuri Kishida), though strictly speaking there are five pure doves born from Mother (awakened) - Yuri Kishida and Kanae - and unawakened doves possessing Mother's essence - Ikuko Kifune, Ryuko Tagawa and Akiko Kiyota. Each of these women has inherited Mother's powers, capable of using special abilities regardless of whether or not they have awoken.
Pure doves, who take orders directly from Mother, have completely different mindsets and morals to humans, but unawakened doves have the memories and emotions of a normal person, so when they become aware of their true self and destiny they suffer over what position to take. When they awaken completely their face changes to that of Yayoi Mikami, the "original", and a face appears on their chest (the dove can choose to hide this if they so choose). They also begin to fear the light (despite having a degree of resistance to it, since their body is generally a makeshift one if they expose themselves to the sunlight for a long time it will eventually melt), and a cruel fate awaits them in their human lives. It appears as though Mother's control over more recently-released doves is stronger than previous ones.
Yamibito Type A
闇人甲式
One of the transformed Yamibito types, created by Yamibito that merge with male corpses and rebuild their bodies in order to increase their combat abilities. With the special ability to enshroud themselves in fog and steal their foe's sight, their shell's strong resistance to firearms (from the front only) and extreme speed and ability to leap several metres at once, they pursue humans with force. However, they are not as intelligent as Type Zero, and their movement patterns are instinctual (though they can say basic things). They hate the light, but have some resistance to it in exchange for sheltering inside a corpse.
Yamibito Type B
闇人乙式
One of the transformed Yamibito types, created by Yamibito that merge with female corpses and rebuild their bodies in order to increase their combat abilities. Their shells are hardened against attacks from firearms (from the front only) and their arms have mutated into bird legs, allowing them to run about quickly, using their swift movements to chase down humans. However, like Type A their intelligence is low and their movements are more instinctive. Their bodies are optimised for the physical abilities that Yamibito seek, but when the cloth is torn from Type A and Type B they are so mutated that they are unrecognisable as humans.
Yamibito Type Zero
闇人零式
A Yamirei that has entered and taken over a human corpse without changing its appearance. They have the same looks and abilities as humans, so they can use various weapons and tools the way people do with little trouble. In addition to their physical abilities that far surpass though of humans they are highly intelligent, easily manipulating the memories of the corpse they inhabit and speak to humans to mislead them. Type Zero is the "base Yamibito form", fitting the image of their shell (human), but Yamibito can freely rebuild their bodies as they wish.