Kai Green

Kai Green is one of Ben's first love interests, who makes her first debut in Benwolf. Kai is the granddaughter of Wes Green, a friend and former partner of Max Tennyson.

Ben 10
She first appeared doing a spiritual Native American dance in the episode Benwolf. She was Ben's first crush, but she only took interest in him after he started becoming Blitzwolfer because she wanted to, as quoted, "train and tame him". When she admitted to this, Gwen gave her a stern talking to. She made a cameo appearance in Ben's dream world in Perfect Day.

Ben 10: Omniverse
Kai appeared in An American Benwolf in London. Working with her grandfather, they find the secret laboratory of Dr. Jekyll, quickly afterwards ambushed by the Forever Knights in their search for Dr. Jekyll's Hyde Formula. While capturing Wes, Kai manages to escape and contacts Ben and his partner Rook for help. Ultimately, they discovered the hidden location of the legendary Excalibur. When removing the blade from its stone seemingly proves impossible even with the Hyde Formula or Ben's strongest aliens, Forever King Chadwick orders his men to kill their enemies. As Ben battles the mutated Forever King, the cave's underground pipes were ruptured and caused a flooding. Convincing the Forever Knights to work together, everyone was able to escape alive.

Powers and Abilities
Kai has considerable tracking skills taught to her by her grandfather. In Omniverse, it is revealed that she has been taking Judo lessons, showing considerable skill against trained soldiers of the Forever Knights.

Trivia

 * In Ken 10 it is seen that Kenny's skin color is a mix of white and Native American.﻿ According to the pop-up version, Ben would eventually marry Kai in a possible future, and she is Ken's mother.
 * In An American Benwolf in London Kai is shown to be the only one able to move the sword Excalibur from it's stone, having grabbed onto it in order to prevent drowning it moved slightly.
 * While still greatly liking Blitzwolfer, she has shown signs of growing feelings for Ben as himself, becoming bashful when people imply they are a couple and giving Ben a kiss on the cheek as he leaves.
 * Kai considers Blitzwolfer to be her favorite out of all of Ben's aliens.