|Age|| 10 (Original Series)|
|Powers and Abilities|
|Abilities||Hand-to-hand fighting skills|
|Relatives||Wes Green (grandfather)|
|Alias|| Little Archaeologist (Ester)|
Mrs. Tennyson (Ben)
|Alternate Counterparts||Kai Green (Ben 10,000 Timeline)|
|Voice Actor||Bettina Bush|
Kai Green is a Navajo girl who 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. She is also Ben's current girlfriend.
In the original series, Kai had long, black hair and brown eyes. She wore a red shirt, green shorts, brown boots with white socks. She had silver bracelets and a blue ring.
In Omniverse, Kai wears a long sleeved red shirt with a red and peach colored sweater. She still has brown boots (now with blue stripes) and her shorts are even shorter now. Her hair is in a ponytail and she also has a tan earring. She wears brown gloves, tan socks, and a belt.
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.
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.
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.
She plays a major role in Fight at the Museum and Secret of Dos Santos. In The Most Dangerous Game Show, Kai has gotten on friendlier terms with Ben, accidentally sharing a kiss but still enjoying it.
Ben 10: Omniverse
- An American Benwolf in London (first re-appearance)
- Fight at the Museum
- Secret of Dos Santos
- The Most Dangerous Game Show
In Navajo, Kai means "Willow tree".
- 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.
- Blitzwolfer is Kai's favorite out of all of Ben's aliens. She also thinks that Pesky Dust is cute.
- While originally only interested in Ben's Blizwolfer form, she has since shown signs of growing feelings for Ben as himself, becoming bashful when people imply they are a couple. She also on impulse kiss Ben on the lips Secret of Dos Santos as thanks.