Familiars can be made from any substance (living, dead, or near death); some objects like dolls and toys can become familiars if given enough life-energy by summoners. True familiars are sown together using parts or dead creatures and plants or even created from fossils and bones. Some humans can become familiars by various reasons such as Kotarou's and Sakuya's over-rewriting of themselves, Takasago's turning the dead parts of his body into familiars, or Akane's brain cells turning into familiars through the disease of the Holy Woman.
Connections between familiars and summoners are forged through a contract (契約, keiyaku).
Types of familiars and levels
- Hounds: The most common Familiars; used by Gaia and random summoners to kill people.
- Leaf-birds: Birds used for scouting from the sky.
- Scout-birds: Used by Akane, can see things from a distance, through thick forests, and allows telepathic communication.
- Mommoths (Chibi Mammoth): Kotori's most powerful familiar, a small mammoth with a powerful body and some have tusks.
- Tree Man: Slow moving trees with faces on them.
- Cintapeed: Over-sized cintapeeds that kill by draining the blood of their victims; even if their prey escapes after being bitten they are likely to die do the the anti-coagulation (Chemical that stops blood from clotting up to stop bleeding) in their venom.
- Nameless Famiiliar: A familiar created by Sakura Kashima and sent to a parallel world in order to kill Kagari. Its body is small but bigger than a rat; a large human eye can be found on its sides and its mouth takes up most of its body. Its has an acidic-like venom that allows it to melt Kagari's ribbons.
- Dima and Lyuba: Two mommoth-like familiars created by Kotarou in the "Moon Route" of Rewrite.
- Berezovka and Woolly: Along with Dima and Lyuba, they are mammoth-like familiars created by Kotori in the Terra Route; Kotori gives them to Kotarou, Kotarou in turn gives them to Akane.
- Wolves: Used by Shimako when saving Kotarou in the forest.
- Leaf Dragon: Tree-like familiar that floats in the sky, attacks people with a hook it shoots from its neck and are powerful enough to destroy several military helicopters in a matter of minutes.
- Fire Spider: They appear in the final phases of Akane's Route. These spiders attatch to their prey and explode into fire.
- Deinonychus: Familiar created by Sakura Kashima in order to kill the Moon Kagari, has the appearance of a red and green rapter-like dinosaur with arms covered with feathers.
- Krivoy Rog: Tenma's familiar, resembols a giant see mullusk; covered in armor stronger than steel. It attacks with its powerful tentacles and can float in the air and fall on its enemies.
- Kilimanjaro: Tenjin's familiar, resembols a giant flying insect. Its wings help it stay out of its oppenent's reach while it fires powerful energy shots from somewhere on its body.
- Fuego: Midou's familiar, a small but powerful lava familiar that can conjure fire at will, repair itself when cut in half and can create a wall of silicone to protect Midou.
- Takasago: A year after being mortally wounded by Kotarou in the forest, Takasago appears and goes on a nearly unstoppable rampage. He had turned all the dead parts of his body into familiars and injects himself with poison that increases his speed and strength, but distorts his body and possible his mind.
- Earth Dragon (Dynamosaurus): Familiar that resembles a T-Rex, but with no arms. Considered to be Gaia's strongest weapon; its skin is thick enough to block Kotarou's blades and its main weapons are its teeth and its tail that can tear enemies apart with one swing.
- Key (Kagari): Dangerous familiar born from the Earth, brought into existence for one purpose, to search for good memories and judge humankind, destroy the world if witnessing good memories is not attainable.
- Sakuya: The strongest familiar and Chihaya's servant.
- Mistletoe: Ancient familiar that hold's its previous summoners memories, intellect, and powers. Once it chooses a person, it turns them into a special summoner called a Druid.
- Tomoko: A Shikigami that Kotarou aquired from Akane.
- Keisuke & Rikako: Kotori's parents who she turned into familiars after the died.
- Pani & Gil: Feral familiars found in the closed space beneath the school that the protagonist and heroines attend, they play a crutial part in the protagonist's development in some routes. (It is also believed that they were actually humans).
- Tree-Gate Familiar: A familiar found in the tunnels of Gaia, its only purpose is to allow passage to the City of Stone. If the familiar is damaged in any way, the way to the city cannot be opened. It also has defensive capabilities; piercing enemies with its branches to defend itself.
- In the Japanese version, familiars are called demons.
- Another term for familiar is mamodo or mamono.