Subtitle: Space Germ (宇宙細菌 Uchū Saikin)
Darii was a parasitic alien monster that travelled to earth and found refuge inside a flower pedal. When a girl named Kaori sniffed the flower, Darii was sucked into her nostril and from there began to take control of her. As the UG did some research and found out that the microscopic Darii was inside of Kaori, Darii used Kaori's body to sporadically enter a trance-like state in her sleep to search for other humans that share the same blood type as Kaori in order to feed on it. Amagi was one of them, and Darii used Kaori's affection to earn his trust, only for the Ultra Guard to force Kaori into an unconscious state until an antidote could be developed to stop Darii from inside Kaori.
Rather than wait, Dan Moroboshi transformed into Ultraseven and shrunk himself down to a microscopic size and entered Kaori himself through her nostril. Upon entering her body, Ultraseven found Darii cling to a wall of her flesh and sipping on Kaori's blood. Ultraseven tried to stop the parasite quickly with its Emerium Beam, but all it did was release Darii from its host and sent Darii on the offense. After a quick stare down with Ultraseven, Darii reattached itself to Kaori's flesh and coated Ultraseven with a white mist attack, which immobilized Ultraseven and making the battle seem one sided. Fortunately the scientists of the Ultra Guard finished the antidote, and injected into Kaori, severely weakening Darii. With the opportunity, Ultraseven used his Ultra Bubble to melt Darii into a pile of foam. With Darii dead, Kaori was freed from the parasite's control.
- Suit Actor: Tetsuo Yamamura.
- Darii's roar would later be slowed down and used by Kingsaurus III.
- The Cinar dub referred to him as the Antroxim-90 virus.
- In the middle-to-late 1990s, footage of Darii was used for the TNT, TBS and Cartoon Network show Cartoon Planet. Darii footage was used to depict an alien in the recurring sketch entitled 'Zorak's Nuggets of Joy' in which Zorak would recite an anecdote from his past or a simple fact of life that he enjoys. In his featured segment, he was called Gandorf the Mad Grinder, under whom Zorak studied in becoming a super-villain. Gandorf, as Zorak's mentor, kept referring to Zorak as little 'Grasshopper'.
- Despite being classified as "Bacteria," Darii's size and body structure would better suit the monster as being a parasite.
- Height: N/A
- Weight: 0.1 g
- Origin: Space
- Powers and Weapons
- Possession: Upon entering the body of its host, Darii can control the actions of its host when they are asleep. The host also can emit a white gas from their mouth that can stun Darii's opponents.
- Freezing Mist: Darii can spew a white foaming mist from its mandibles, it can immobilize Darii's opponent.
- Exoskeleton: Darii's exoskeleton is strong enough to withstand Ultraseven's Emerium Beam without showing any sign of damage.