Girl Tiri is what resulted when Tiri was effected by an explosion of a molecular altering device, he was attempting to use to discover a better method of Terraforming. It instead rearranged his genetic code knocking out the y chromosome, and duplicating the X (actually tripling it but one was destroyed). In order to return Tiri to his natural state, Scientist Kaviatiri Delki needed to construct a similar device to manipulate the Y back into place. This took a whole Earth Month.
Tiri was already high energy, and this carried over. He became extremely "girly" and "giggly" after the accident. He also started to feel female emotions and loved that he could appreciate nature more. However he decided through this insight to quite the warrior job class for a while and become an explorer of foreign worlds. Akiti had also quite by this time as the Intergalactic League of Planets was forming, and he wanted to join the resistance. He and his girlfriend seemed to act more like close friends than in a relationship.
He developed breasts, different body structure, larger hips, and different genitals. For some reason, in this form, he was not bisexual like all other Karkans, but attracted to males only, possibly due to genetic damage. His clothes looked bad on him, and he still retained his want to look good at all time so Luno lent him some of her clothes and so did Sarah.