The first Daimon on Earth was Germatoid, who crossed over from the Tau Star System and infected the scientist Professor Souichi Tomoe, overriding his personality. The possessed professor then established Mugen Academy and the Death Busters, intending to find the Holy Grail and facilitate Pharaoh 90's passage to Earth. As part of his operation, he produced more Daimon Eggs and began to experiment with the creation of further Daimons.
In the anime, the earliest known Daimons to be created by the Death Busters were, like Germatoid, fusions with humans. However, the only known fusion of this type, created from an unwilling Mugen Academy student, was apparently not as efficient, and resulted in an enormous, limbless creature with sharp teeth. Despite its ungainly appearance, it was extremely powerful. After being hit by Sailor Neptune's Deep Submerge attack, the Daimon was destroyed and the host reverted to human form, apparently unharmed.
Later methods of Daimon creation involved the fusion of a Daimon Egg with another (usually inorganic) object. As soon as the target touched the object the Daimon would awaken, transforming into a creature based on the object before trying to extract the Pure Heart Crystal out of its target. As the production process was refined, Daimons became more powerful. Beginning with those used by Mimete, Moon Spiral Heart Attack was too weak to destroy them, and Sailor Moon had to use the Holy Grail and Rainbow Moon Heartache in order to defeat them.
When Daimons were defeated by Moon Spiral Heart Attack, they usually cried, "Lovely!". When they were defeated with Rainbow Moon Heartache, however, they instead usually cried, "Love-lovely!". For a short time in the English dub, the Daimons also cried "Lovely!", but this was not continued.
In the manga, the Death Busters removed the souls of beings on Earth and used their empty bodies as vessels to hold beings from the Tau Star System. Most of the Daimon Eggs were implanted in Mugen Academy students, though there were also examples of them being used with cats and dogs. When the Daimon implantation failed, the one so affected would revert to a monstrous state.
Every Daimon except for Haikyun appeared in the video game Quiz Sailor Moon - Chiryoku Tairyoku Toki no Un. There was also a Daimon named Quiz who was unique to the games Sailor Moon S: Quiz Taiketsu! Sailor Power Ketsushuu for Playdia and Sailor Moon S - Kotaete Moon Call for Telebikko.
Many Daimons from the anime could be encountered as enemies in Sailor Moon: Another Story. An optional boss in chapter three resembled a failed Daimon from the manga, and appeared to be controlling Professor Tomoe, though its origins were unclear.
- The name "Daimon" likely came from the daimon (or the Latinized version "daemon") of Greek mythology.
- The final series of Daimons, which were all commanded by Mimete, had names that started with "う" ("u" in romaji). This could have been a reference to ukai, a fishing method in which cormorants are used to catch fish by swallowing them and then being forced to cough them up, as Professor Tomoe mentioned ukai fishing in his explanation of the new Daimons to the Witches 5. This series of Daimons swallowed the captured Pure Hearts after extracting them from the victims, in an attempt to prevent them from being taken back by the Sailor Senshi.
- In the first English dub, the Daimons were called "Heart Snatchers."
- In the German dub, the last word the Daimons said was "Verloren!" (I lost!).
- In the Italian dub, when Daimons were destroyed they said "Per me è finita!" (For me it's over!).