|“||Did it sound like she missed me?||”|
They first met during Welcome to Paradise, after Kai attempted to kill Damon in order to reawaken Bonnie's magic. Ever since they met in the 1994 Prison World, Bonnie loathes Kai. After the several atrocities Kai has committed against other innocents, including herself, Bonnie imprisons him in another Prison World. She did this to punish Kai for all his crimes against those she cared about and for those who were innocently killed because of Kai.
They are known as "Bonkai" by fans.
Throughout The Vampire Diaries Series
Bonnie first meets Kai in Welcome to Paradise, when he attempts to kill Damon. She threatens him, but he immediately mentions her inability to practice magic and proceeds to stake Damon. Just then, Bonnie's powers return when she lights a candle and she surrounds Kai with a wall of fire. Damon uses this to knock him out.
Later on, they watch on as he wakes up and questions him on why he tried to kill Damon. He finally reveals that he only did it to ensure that Bonnie would get her magic back.
In Black Hole Sun, Bonnie, unlike Damon seems more comfortable around Kai, even releasing him despite Damon's orders not to. After Kai convinces Damon to talk about his life in 1994, Bonnie is shocked to discover that he killed a pregnant woman.
Later on, Bonnie and Kai are seen trying to locate the Ascendant, though Bonnie is unable to do it, claiming that she doesn't feel comfortable. Damon immediately insults her by saying she sucks at magic which is when Kai jumps in, claiming that Bonnie should just ignore Damon. They flirt with each other for a few moments before Damon interrupts them with another remark.
Later on, Bonnie is confused when her spell starts leading her directly to Mystic Falls despite the Ascendant supposedly being in Oregon. As she realizes Kai has it, she places her hand on his chest and all of the candles flicker, confirming her suspicion. Kai then finally mentions that he just tried to see if Bonnie's magic was precise and then claims that they're ready to go home.
Later on, Kai is seen in the front yard, trying to determine the location of where to harness the eclipse's power. Bonnie immediately mentions how he shouldn't have wasted their time with the locator spell to which he replies that he just wanted to feel her hand on his chest. Bonnie and Damon bicker about him and then as the two men continue walking, Bonnie takes one of the folded newspapers and remembers Kai mentioning something about having many sisters and brothers. This she connects to the family massacre explained in the newspapers.
It turns out that Kai's real name is Malachai and that he is actually a witch, a powerless one as well as the murderer of his own siblings, much to Damon and Bonnie's shock. Bonnie immediately refuses to do the spell despite Damon's pleading. Kai is upset by this turn of events and tries to grab Bonnie, only to get attacked by Damon who was defending her. Later on, Damon and Bonnie plan on how to get back without Kai when he shows up, claiming that his special ability is to consume a witch's magic temporarily, though to the point of their death. He demonstrates this when he grabs Bonnie and channels her magic by setting the stove on fire and giving Damon an aneurysm while at the same time keeping Bonnie in a lot of pain due to using her magic. He then explains that if they don't all work together, he'll drain Bonnie's magic, kill her, and then do the same to Damon. The other option is for them all to go back together as allies and friends.
In The World Has Turned and Left Me Here, Bonnie and Damon are walking through the woods to meet up with Kai, while they discuss him and his intentions. He quickly shows up and Bonnie asks him to show her the spell, though he refuses and heads off to gather some supplies. After returning, Bonnie refuses to do the spell until he actually shows it to her, though he refuses to show her the spell. The two eye each other angrily for a few moments until Bonnie finally challenges him to just absorb all of her magic and kill her as she won't do the spell. Kai at first is hesitant, but then grabs her and starts draining her magic painfully, with Bonnie fighting back. After some time though, he releases her and she then realizes he can't kill her because he doesn't know the spell.
She figures that they don't need him and telekinetically shoves a pickaxe into his chest, killing him. After figuring out that she is the key to getting back, Bonnie and Damon prepare to return, but then Kai shows up and quickly shoots her with an arrow to stop her. While he and Damon fight, Bonnie uses her magic and sends Kai a few yards back. She then proceeds to send Damon back to the mortal plane, while sacrificing her chance of getting back.
The Ascendant is destroyed in the process and Kai angrily screams, realizing he is stuck there, possibly forever. Meanwhile, Bonnie cries, happy for Damon but sad for herself and then passes out from the bleeding wound, while now trapped with an enraged Kai in the time dimension.
In Do You Remember the First Time?, Kai has taken Bonnie back to the Salvatore Boarding House and has treated her wound. He is then seen trying to fix the Ascendant while Bonnie's lying on the couch, unconscious. After she finally wakes up, he asks her if she's okay and then assumes she's going to help him with fixing the Ascendant. She however refuses which forces Kai to demonstrate his power over her by grabbing her hand and so he starts draining her of her magic.
Bonnie however grabs a pen from the table and stabs him in the neck, which kills him temporarily. She then proceeds to get all of the parts of the Ascendant and runs out, with Kai dead on the floor. Bonnie eventually reaches the hospital where she treats her wound and manages to fix the Ascendant, only to realize she's missing one piece. Suddenly, all of the lights shut down and Kai appears with the last piece. As he slowly moves towards her, Bonnie reacts by destroying all of the objects around him which slows him down.
She then runs back to Damon's car only to be unable to start the engine. Kai shows up in the backseat and grabs her from behind. She tries to fight back but is unable to and Kai forces her into getting them home.
They're later seen in the cave, awaiting the eclipse. Kai then reveals that he's brought her a "gift" - Ms. Cuddles, thinking she wants to bring her childhood toy along. He then starts talking about how he wants to be a better man - patient, loyal and good - like Bonnie. Bonnie cuts him off and says that they should just go home. He gives her the Ascendant and she starts performing the spell. As he grabs her hand, she lets a little of her blood fall onto her teddy bear. Suddenly though, she stops the spell, claiming she's lost her magic.
Kai then grabs Bonnie only to realize there's no magic left in her. He then tries to figure out what happened, only for Bonnie to reveal that she placed all of her magic somewhere safe.
Kai realizes it's in the bear though then finds out that it was sent back to the mortal plane. He starts yelling to which Bonnie responds by provoking him even more as she says that they're stuck there forever.
In Fade Into You, Kai kidnaps Bonnie by drugging her with pain killers. He then takes them both to Portland, Oregon, to his family home. He drags Bonnie out of the trunk and she starts wondering where they are. After he cuts the rope around her hands, he reveals to her they're in Portland, and she starts complaining, claiming he could have taken her anywhere in the world yet he took her to Portland. He claims it's Thanksgiving in the real world and that he's gonna make Bonnie dinner.
As they near his house, Bonnie questions him on why he wanted to come here, to which he responds by saying he wanted to finally show his house to someone. They're later both seen in the kitchen, with Kai making them dinner while Bonnie plays with his pager, though he quickly takes it from her, claiming he doesn't want her to bust it. Bonnie then finally mentions how she doesn't want to spend the rest of eternity with him, claiming she will never like him or enjoy his company, though he claims he wants to apologize for everything. She however claims they should divide the world in two and separate. Kai finally accepts the deal, claiming he'll even give Bonnie his car, though only if she has one last dinner with him. She happily accepts. They're later seen eating, with Bonnie boringly starring at Kai as he eats the same piece for 45 minutes. She tells him to quit stalling and give her his car keys though he continues stalling by telling Bonnie who actually sent him to the prison world they're in - his father. They then finally walk outside, with Kai explaining the events of the night he was banished. They walk over to a tree stump and Kai finds the knife his sister imbued with her magic, still there. He drains the knife of Jo's magic and reveals how he needs Bonnie's blood for the spell. He then quickly stabs Bonnie and leaves her there, lying on the grass. Bonnie later on wakes up, realizing he lied to her about letting her go peacefully and giving her his car.
In The Downward Spiral, Kai expresses his wish to see Bonnie to Damon, feeling bad for everything that he's done to her during their time in the prison world, including emotional, physical and mental damage, so he blackmails Damon into setting up a meeting between Kai and Bonnie in order to find out more about his imprisoned mother. Bonnie however immediately tells Damon not to bring Kai over to her, still angry at him for what he did to her in the prison world.
Damon however brings Kai to Bonnie at the rave, where Kai apologizes to Bonnie for everything that he's done to her. Instead of accepting his apology, Bonnie remembers all of the horrible things she's suffered at his hand and threatens to melt his face off if she ever sees him again. She then leaves in furry as Kai watches on, disappointed and sad that she reacted this way. Meanwhile, all of this leads to an argument between Bonnie and Damon too, where she punishes him for bringing Kai to her.
In A Bird in a Gilded Cage, Bonnie at first refuses Damon's request to help them travel to the 1903 Prison World, due to their argument that took place the night before. However, Damon promises her that she will want to come after hearing what he has in mind. Later on, Bonnie is seen in a diner with Kai, asking him for the 1903 Prison World Ascendant. He toys with her at first, though soon shows the Ascendant. He then makes a deal with her that he will help them only if Bonnie goes along. She agrees reluctantly.
Later on, over at the Salvatore Boarding House, Bonnie and Kai are preparing the spell to transport themselves together with Elena and Damon into the Prison World when the latter two show up, ready to go. Kai and Bonnie then perform the spell together, in order to transport all four of them. Upon arriving into the Prison World, Elena and Damon head to Lily's house, leaving Bonnie alone with Kai. Bonnie then proceeds to perform a fake locator spell in order to locate the prison's ascendant by using Kai's blood. As she's chanting, Kai starts apologizing to her, wanting her forgiveness for what he's done to her. She however doesn't pay any attention to him which upsets him to the point where he grabs her roughly, interrupting her spell. Bonnie then explains that even if he has changed, he has still retained some of his old negative traits.
The two then head off into the woods, in search for the Ascendant where Kai starts wondering if Bonnie's spell is right. She then tells him that maybe she does believe in him changing much to his joy, though he doesn't realize that she has tricked him and manipulated him into trusting her only to literally stab him in the back, much like he did to her in the Prison World. As she stabs him from behind, Kai continues pleading with her, claiming he's changed. Bonnie however ignores this and after stabbing him in the back two times, she attempts to stab him in the heart this time, claiming she has changed too. Before she is able to kill him, Kai disappears. Later on, as Bonnie is performing the spell to leave the Prison World with Elena, Lily and Damon, Kai shows up, too late though, screaming Bonnie's name in hopes that she would change her mind. She only smiles at him, happy that she's gotten her revenge as the spell takes effect and sends them back to the real world, leaving Kai trapped.
In I'll Wed You in the Golden Summertime, Bonnie had nightmares with Kai and Lily. She dreamed that Kai scoffed at her and said that while she was asleep, he lay next to her and siphoned all of her magic. As Lily attacks Bonnie in her sleep, the latter runs out and into Kai, who claims that he siphoned all of her magic. Later on, Bonnie takes this dream as a prediction and in search of Lily together with Matt ends up subdued by an invisible force (later revealed to be Kai) that leaves her bleeding from the wrist. It later turns out that it was Kai who attacked them, in order to keep Bonnie from interfering with his plans to get his revenge on her and his coven.
In I'm Thinking Of You All The While, Bonnie awakens in the Salvatore Manor, aware that it was Kai who attacked her and Matt. After searching around the house, Bonnie and Matt find a video recorded by Kai, in order to let the gang in on his revenge plan. In the recording, Kai mentions that he was actually hurt by Bonnie's betrayal when she imprisoned him in the 1903 Prison World, therefore as revenge, he bound her life to Elena's, ensuring that Elena will be in a magically-induced coma as long as Bonnie is alive. Bonnie, aware that there is no loophole to Kai's curse, went to where the wedding took place. Once there, she finds a room full of dead Gemini witches, and a newly-made vampire Kai, weakened by Tyler's werewolf bite, in search of blood. Bonnie then magically attacks him, by giving him an aneurysm and breaking several of his bones. Kai though siphons the magic of his werewolf bite and sends her flying into the wall, injuring her fatally. Damon shows up later, and finds a dying Bonnie on the floor, with Kai who tries to talk him into killing the former so that Elena would awaken. At first, Damon pretends like he chooses Elena's life over Bonnie's, leaving a devastated Bonnie and a surprised Kai, who hoped that Damon would first be conflicted between who to save instead of immediately choosing Elena. As he's telling this to Bonnie, Damon appears behind him and chop off his head, killing him.
In It's Been a Hell of a Ride, Bonnie and Kai were reunited shortly in 2018, 5 years after his death when he linked her life to Elena's and killed the entire Gemini coven. This was due to the ringing of the Maxwell bell which allowed Kai to escape Hell.
After his attempt to kill Lizzie and Josie Saltzman, Caroline snapped his neck and he was given to Bonnie, who then empowered and aided Lizzie and Josie in creating a new 2018 Prison World for Kai. Bonnie visits him in the Prison World and torments him about his permanent imprisonment in the new prison world. Kai meanwhile reveals to Bonnie that Katherine is back from Hell as well, having came to control it after Cade's death. Bonnie leaves him quickly after this, and he is left screaming her name, having been left alone in the prison world, his worst fear.
- They are both witches, although Kai does not have his own magic unlike Bonnie, making Kai a Siphoner.
- Bonnie was the first witch in more than 18 years to fall victim to Kai's magic-draining powers, though he did not drain her power completely, instead he only did so as a demonstration of his abnormal power.
- Kai was the one who caused Bonnie's magic to awaken by threatening to kill Damon.
- They have both acted against their own kind and killed another witch; Kai slaughtered his entire family of witches (for no apparent reason) while Bonnie killed Kai and has tried to kill a coven of witches while under Silas' control.
- Both have attacked each other; Bonnie stabbed Kai with a pickaxe and later on, he shot her with an arrow. He also later on stabs Bonnie in order to use her Bennett blood.
- As of The World Has Turned and Left Me Here, Bonnie is trapped with Kai in the Otherworldly Time Dimension, with no way out as the Ascendant was broken when Bonnie sent Damon back. Bonnie fixed the Ascendant in Do You Remember the First Time?, but she stored her magic in her childhood teddy bear, Mrs. Cuddles, so that neither she or Kai could leave.
- In Fade Into You, Kai stabs and leaves Bonnie alone in the Prison World, using her blood to return the mortal plane. He leaves her there as revenge for her sending his magic away.
- In The Day I Tried To Live, Kai helps Elena, Damon, and Jeremy to bring Bonnie back.
- They have both stabbed each other and left one another trapped alone in a Prison World: Kai left Bonnie trapped in the 1994 Prison World created for him while Bonnie left Kai trapped in the 1903 Prison World created for Damon's mother.
- In A Bird in a Gilded Cage, Bonnie is shown to be significantly stronger than Kai who is the Gemini Coven Leader. When Bonnie takes Elena, Damon, Lily and herself back to the Real World without any signs of struggle or strain, whereas in The Day I Tried To Live, Kai took Elena, Damon, Jeremy and himself to the Prison World, he quickly weakened after a couple of minutes resulting in his nose bleeding, making everyone return back to the Salvatore Boarding House.
- However, over time Kai had gotten much more powerful than before, as Bonnie could not lift the spell that made Elena sleep as long as she lived. By the time he became a Heretic, having his vampirism to siphon to draw magic from, in I'm Thinking Of You All The While, Kai was easily able to defeat Bonnie, telekinetically lifting and severely wounding her without her being able to do anything to break free.
- However, by the end of the series, Bonnie, after re-acquiring her powers, has surpassed Kai, as she successfully undid his spell and woke Elena without having to die, although it is never shown how she compares to Kai as a Heretic.
- Both have trapped one another in all three Prison Worlds at one point for revenge; Kai stabbed and left Bonnie in the 1994 Prison World after terrorizing her, Bonnie later manipulated Kai into thinking that she was going to forgive him and then trapped him in the 1903 Prison World. After his resurrection in 2018, Bonnie trapped him permanently in the 2018 Prison World as revenge for all his actions against her and her friends.