- Full name: Kaikaina Grif
In episode 81, it is revealed that a tapping noise inside the large ship that dropped into the gulch has been coming from Grif's sister, who is referred to as "Sister" by both teams. She tells the Reds she joined in order to be reunited with Grif, and that Command had sent her as a new recruit since one team member will be promoted to replace their deceased commanding officer. She did not age on her 800-year journey due to the effects of the theory of relativity in traveling near light speed. It is revealed in episode 84 that she is color-blind, and thus enlisted in the Blue Army by mistake. In episode 85, Grif releases her to the Blue Team in order to protect her from Sarge, and in the next episode the Blues give her an orientation but are interrupted by Tex firing at them. When Tex calms down, she expresses indignation at the fact that the Blue Team has acquired a new girl after she'd only been gone for a few weeks. In episodes 88 and 89, Tex and Sister have a private conversation while Church and Tucker discuss the consequences of having two girls on the team.
Soon after, Doc says that he needs to give her a physical due to her being a new soldier; Tucker is left jealous at the fact that Doc was giving her a physical while she was naked. Meanwhile, the Red Team, who are underground at the time, find some surveillance equipment and see her naked, infuriating Grif but intriguing Sarge and Simmons, while Donut is interested in the room's decor. When Church follows Vic Jr's orders to attack the Reds, he sends Doc, Sister and Junior into the caves as per his orders. In the caves, the trio find Lopez's disembodied head, and as they talk to him, they are approached by a new Alien and its friend, a very much alive Captain Flowers. She, Doc, and Junior are then held captive by Flowers and the new Alien in the underground cavern, until O'Malley leaves Flowers's body in episode 100.
Sister is the only remaining Blue soldier in the canyon come Reconstruction. She apparently throws raves every night, charging five dollars per person, being ecstatic at the fact that she only had two attendees. She is quite useless to Washington, whom she assumes is a cop.
In episode 3 of Relocated, when Sarge calls Lopez to tell him to relocate to the new base, Lopez informs Sarge that he has killed Sister and won the battle in Blood Gulch in favor of the Reds. When Grif is informed that Sister is dead, he refuses to believe it on the grounds that Sister had previously survived being trapped under ice in a freezing river for three hours, and had been pregnant when pulled out.
A running gag throughout her appearance in Season 5 is that she would always confuse other characters with unbelievably ridiculous comments. Such includes comments about attempting Aspirin overdose and surviving, having the ability to ejaculate, and having seven abortions.
Although Rebecca Frasier was a good friend of the Rooster Teeth production crew, Burnie Burns intended to allow other women to audition for the role of Sister despite the pressure from the other members. He notes two other girls auditioned for the role before Frasier was given her chance, but when she began auditioning the team made something of a joke out of the audition, slipping in more and more lines of dialogue which got increasingly more vulgar to see how far Frasier would go before refusing to do a line. Upon realizing she had no such limits, Frasier was cast as Sister and the role was re-written as a far more promiscuous character to fit with the lines she had read in the audition.