|“||You’re going to merge with me.||”|
It was revealed in Fade Into You, that they were born in Portland, Oregon, in the 1970's, as a pair of twins for the Gemini Coven. Different from the rest of his family, Kai was born with no magical power of his own but was gifted with the ability to absorb the power of others. Based on the tradition of the coven, only a set of twins would become leaders, hence their name "Gemini".
On the other hand, at the age of 22, the twins have to merge power. The stronger one would absorb the power of the weaker, who would die as the result. Realizing Kai's disability, the Parker family kept having children until another set of twins were born. Luke and his sister Liv entered their lives as the 7th and 8th children of the family and the 2nd set of twins.
Kai killed 4 out of 7 of his siblings, attempted to murder the twins, but failed because Jo protected them.
Throughout The Vampire Diaries Series
In Christmas Through Your Eyes, Kai is seen at the cemetery with Luke and Liv. Luke intervenes, trying to stop his brother after he stabs Jo again. Kai then shoves Luke into a wall and reminds him that he wanted to kill him when his brain was the size of an acorn and he doesn't have a problem doing it now. Luke shoves Kai away from him and walks out, saying he will not watch the current events unfold. Kai laughs after he leaves, shoving more signs of sociopathy in his eyes calling Luke "dramatic", much to Liv's visible annoyance.
In Prayer For the Dying, Luke intervenes in the Merge between Kai and Jo, and offers to merge with Kai instead. Due to the fact that his imprisonment had kept Kai at the age of 22 and that they were of the same bloodline, it provided the needed loophole to allow them to attempt the Merge. Luke dies during the Merge and Kai now has permanent magic.
In The Day I Tried To Live, it appears that since Luke and Kai merged, they are one and the same. Kai attempts to kill Liv but is unable to do so due to the part of Luke that reignites in him. Not only this but Kai confesses to Elena that Luke is having an impact on all of his emotions as he admits that he wrote a letter of apology to Jo, and then he began to cry which confused him, but this is due to Luke's humanity.
- Kai did not want to merge with Luke, however he was forced by Luke to merge.
- Kai was responsible for Luke's death.
- Luke and Kai are not twins, however they were able to merge due to them being from the same bloodline and biological age.
- After the merge, Kai feels remorse for killing Luke.
- Kai also started to experience emotions that he would not regularly feel on his own. Luke's emotions fused into Kai to give Kai his own, new emotions, after the Merge.