PLAYED BY: Kim Darby
SPECIES: Human Female

Adolescent girl on a parallel Earth hundreds of light years from the Federation's, Miri's parents, along with all the other adults on her planet were killed by a mysterious virus that affected only the post-pubescent in an attempt to extend the life expectancy. As a result of the miscalculation, the virus wiped out the entire adult population very quickly, leaving only children, who would age only one month for every one hundred years of real time. As a result, Miri was over 300 years old in actuality. She befriended Captain Kirk when his landing party was quarantined on the planet surface. However, it was in fact a deception, as Miri, along with all the other children ("onlies"), did not trust adults ("grups") after what happened to them. When Kirk revealed the truth about what was happened on her planet and showed Miri that she too was infected with the disease, she took him to confront the other children who had stolen the landing party's communicators. With the communicators recovered and the children trusting the landing party, they were able to contact the Enterprise and develop a vaccine, thus saving the children and the Starfleet crew. Although she was secretly in league with the other children, Miri really loved Captain Kirk.

PLAYED BY: Michael J. Pollard
SPECIES: Human Male

PLAYED BY: Stephen McEveety
SPECIES: Human Male

One of the onlies on Miri's planet, the "Bonk-Bonk" Kid's name is never revealed, but he had an affinity for knocking on objects with a hammer and yelling "bonk-bonk." One of the more aggressive children in Miri's group, the Bonk-Bonk Kid attacked Captain Kirk with a wrench, cutting him open. When Kirk pointed out the blood on his face and the blood on the Bonk-Bonk Kid's hands, the children realized that they had became everything they hated about the grups.

PLAYED BY: John Megna
SPECIES: Human Male

Jahn's friend was an onlie that lived on Miri's planet and suffered from the life prolongation complex. He was Jahn's best friend and followed him without question. Jahn's friend enjoyed being the center of attention, and role-played as authority figures including a teacher and a policeman. He was usually one of the first to suggest punishing others, and fostered a mob-mentality through his chanting of "Bonk! Bonk!" and the like. He carried a wrench that he used to bludgeon Captain Kirk.

PLAYED BY: Ed McCready
SPECIES: Human Male

One of the oldest onlies on Miri's planet, The Creature was stricken with the deadly disease that infects all adults on the planet's surface. Beliving Dr. McCoy was stealing his tricycle, he attacked him, but was quickly subdued by Captain Kirk. When Kirk claimed he wanted to help him, The Creature called him a liar and died shortly after.