Holio, despite his destructive function, has an eerily calm nature when he is not active as a black hole. This is deceptive at first glance, for behind his harmless appearance belies his more chaotic abilities. When not using his powers, Holio is very compliant with demands and eager to help clean up debris as his one true place. He is also shown to be loyal and helpful to his friends, joining Stitch's rebellion to fight off Gantu.
Experiment 606 was the 606th genetic experiment created by Jumba with Hämsterviel's funding. He was designed to create a matter-sucking black hole capable of sucking in entire planets. 606 and the other first 624 experiments were deactivated and smuggled to Earth by Jumba during his mission to capture Experiment 626.
All of the experiment pods were released and scattered across the island of Kauai.
606's pod eventually made its way to a jewelry maker, who attached the pod to a bracelet as a charm.
An elderly vendor fashioned and sold the bracelet to Mrs. Edmonds, which she bought as a birthday present for her daughter, Mertle, neither of them aware of what the experiment pod attached to it actually was.
During Mertle's birthday party, Lilo and Stitch pulled a harmless prank on Mertle and the hula girls. Lilo then noticed 606's pod on Mertle's bracelet and tried to take it from her, only to get in trouble with Mrs. Edmonds and Nani.
Later on, Stitch went undercover as a bunny at a pet shop, where he inspected the pod number on Mertle's bracelet and radioed Lilo via walkie-talkie. After Lilo looked up 606 and learned about the latter's powers, she fell into despair, but got arrested for being in Officer Kahiko's car (though Stitch bailed her out).
Despite Lilo and Stitch's best efforts to steal Mertle's bracelet, when she discovered that Lilo was desperate to stop 606's pod from getting wet, she took the bracelet back to her house. There, out of curiosity, Mertle dropped the bracelet into a glass of water, getting the pod wet and activating 606.
606 then created/transformed into a black hole, which began to suck up everything in Mertle's bedroom. After a while, the hole expanded beyond Mertle's room and started sucking up the entire town. Mertle eventually telephoned Lilo to complain about the massive destruction that 606 was causing.
Fortunately, Lilo and Stitch (with some of Jumba's assistance) were able to enter the black hole in Nani's dune buggy and throw an anti-antimatter sphere into the center of the hole, causing it to begin to collapse.
Lilo and Stitch managed to narrowly escape the black hole, which released everything that was sucked in except Mertle's dolls. She then demanded her dolls back from 606, who complied by releasing the countless dolls through his mouth on top of Mertle.
Shortly after, 606, named Holio, was found a one true place sucking up construction debris while repairs were made to the Rental Hut.
Holio was briefly seen in "Snafu", creating a black hole to suck litter off the streets.
The first 624 experiments, including Holio, were rounded up by Leroy and taken to a stadium to be destroyed. However, Lilo, Stitch, Jumba, Pleakley, Reuben and Gantu arrived before the experiments could be destroyed.
Holio did not participate in the following battle between the experiments and the Leroy clones, instead choosing to retreat with the weaker experiments. However, in one scene, Holio can be seen around some of the Leroys as they started to shut down.
The Leroys soon gained the upper hand in the battle, but were defeated when Lilo, Stitch, Reuben and several other experiments performed the song "Aloha ʻOe", which caused the Leroy army to shut down due to the original Leroy's fail-safe.
- Holio was first revealed in a DVD bonus feature of Stitch! The Movie in the experiment gallery.
- Holio is not referred to by his new name at any point in his debut, but his name officially appears on the experiment name list in Leroy & Stitch.
- In his episode, Holio has no tail, but in "Checkers", when he and the other experiments jump ashore, he is seen with a stumpy tail.
- Holio's pod color is blue.
- Holio is described by the experiment computer screen as, "Experiment 606. Primary function: Creates black holes."
- In Leroy & Stitch, Holio did not participate in the battle between the Leroy army and the experiments, which is ironic, considering that he willingly rebelled against Gantu in "Checkers".
- Holio's head appears in the online game Jumba's Lab.