Caitlin and Cisco meet for the first time in S.T.A.R. Labs when Cisco is hired in January 2013. Cisco is given a tour by Hartley Rathaway, who immediately feels threatened by Cisco and establishes an acrimonious relationship with him, in spite of Cisco's friendly demeanour. Caitlin remarks casually that Hartley seems to have met his match in Cisco's brilliance and introduces herself. Cisco eyes follow Caitlin as she leaves the room. He smiles and comments on how nice she is. They like one another immediately and become fast friends, along with Caitlin's boyfriend (and later fiancé) Ronnie Raymond. The three of them become really close friends and work together with "Harrison Wells" on the particle accelerator. In December they are ready to launch, but something fails and causes an explosion, which kills Ronnie as he tries to stop it.
Following the catastrophe and its effects on Central City, all the employees leave S.T.A.R. Labs with only Caitlin and Cisco remaining with "Dr. Wells", who is now in a wheelchair. Caitlin and Cisco are there for each other as they mourn Ronnie, and a few weeks later Wells brings Barry Allen to the labs for the three of them to care for as he suffers a coma as a result of the explosion. They meet Felicity Smoak, who comes to visit Barry in January 2014. In April, Caitlin and Cisco are tasked with taking inventory of their S.T.A.R. Labs facility in Starling City, after Starling cancels the lease on the building. Cisco tries to remind Caitlin that the explosion was an accident, but she is still suffering from the pain of losing Ronnie.
They are attacked by Slade Wilson and narrowly manage to escape with the help of Cisco's handling of a weapon designed by Arthur Light who was fired by Wells in Spring 2012 for making crazy things. Felicity and Diggle go to the scene and meet a shaken Caitlin and Cisco, who won't reveal what Slade took as they don't know that Felicity and Diggle actually work for Green Arrow.
Cisco and Caitlin join Team Flash as Barry decides to become a masked hero to protect Central City. When Caitlin discovers Ronnie might be alive she goes to Cisco. Something Caitlin will continue to do throughout the series, showing how close their bond is. Cisco and Caitlin investigate finding “The Burning Man” a.k.a Ronnie. Cisco holds Caitlin as she cries over Ronnie being someone she no longer recognizes. The intimacy between them shows how much Cisco cares for Caitlin.
When Caitlin is taken by Captain Cold. Cisco is extremely concerned and he rescues her, along with Joe, letting her know he will never let anything happen to her. Cisco feels guilty about Ronnie’s death the night of the particle accelerator explosion and he opens up to Caitlin, who eases his burden, letting know it isn’t his fault. They later giggle and share ice cream together in a nice moment between them. When Cisco is abducted Caitlin is worried about him. It mirrors his concern for her when she was abducted. When Cisco is saved, Caitlin is overjoyed.
Similarly, again later in the season Cisco gets into a few scrapes, when stung by meta bees, Caitlin is worried and runs over to him. Again, when almost attacked by Bates, Caitlin runs over to Cisco to make sure he's okay. 
Cisco continues to be the main support for Caitlin as she mourns the loss of Ronnie. Their friendship continues to go from strength to strength, as they assist in Team Flash to help save Central City. Cisco observes Caitlin's bond with Jay and comments on it the most. Meanwhile he himself starts a budding relationship but it ends as quickly as it started. Unfortunately for Caitlin, it turns out Jay is actually Zoom and he betrays her. Barry finds out that Caitlin helped "Jay" with the Speed drug and is angry. Cisco jumps to Caitlin's defense and the team quickly move on from the incident. Cisco is Caitlin's rock as she deals with first "Jay's" death and then his betrayal. Cisco is the only one incredibly concerned about Caitlin's possible future as Killer Frost. He worries about it when travelling to Earth-2. He pleads with Earth-2 Killer Frost and insists that he shares a bond with her. Ultimately, she betrays Zoom, no doubt because of the conversations she had with Cisco who seemed to believe in her redemption. Also when she finds out about Jay's betrayal and is kidnapped, Cisco is frantic as Zoom carries her out the Lab. Cisco helps Caitlin deal with the trauma of being kidnapped. In a tender moment she leans on him for support.
As she talks him down she reminds him of the times he helped her when she was struggling. Constantly through the show Cisco and Caitlin are able to get through to one another and share things which they don't share with anybody else.
Cisco eventually comes to accept his brother's death and spends the second half of the season being consumed with trying to save Caitlin from turning into Killer Frost. He and Julian, who she is dating, clash over what is best for her and how to help her. Cisco's only focus is Caitlin. Afraid of a future prophecy that he and Killer Frost will battle to the death. He is desperate to save Caitlin. Cisco is rather snappy with Julian who seems to believe he knows what's best. Whereas as Cisco being her long time best friend and confidant is grappling with what he believes will help Caitlin the most. Caitlin "dies" and Cisco wishes to respect her wishes of not turning into Killer Frost. As Caitlin flatlines, Cisco cries in absolute distress over the "death" of Caitlin. Julian disregards Caitlin's wishes and rips off the necklace to revive Caitlin, causing Killer Frost to emerge. Leading Cisco and the others to believe the prophecy which suggests that Cisco will have to destroy Killer Frost to stop her will come true. This scares Cisco as he says he doesn't want to hurt her. While Barry is focused on saving Iris, he runs to the future to learn clues about Savitar's identity. There he meets a future Cisco who lost his hands during his battle with Killer Frost. There we find Killer Frost has been imprisoned. As the Team visit her we see future!Cisco visibly shaken by the sight of Killer Frost imprisoned. He has no hatred towards her, only pity, which reinforces Cisco's devotion to Caitlin.
When Killer Frost is forced to enlist Team Flash's help. Cisco and Killer Frost bond and reminiscence. He reminds her of moments they shared before they were ever part of the Team. Cisco recalls a funny line that Ronnie said and Caitlin finishes it off. It's the first moment of humanity we have seen from Killer Frost which only Cisco could draw out. They share a moment. Later, Cisco, along with Barry and Julain plead for Cailtin to stay. She responds that she never loved any of them but there is a flicker of emotion as she gets into the elevator. No doubt brought on by the initial moments that began to thaw her heart with Cisco. During the final battle with Savitar, Barry says he will go get his girl (Iris) and Cisco will do the same in getting Caitlin. He begins to battle with Killer Frost but ultimately stops. Once Savitar's plan to murder Iris goes awry, Cisco is kidnapped by Savitar. In his lair, Savitar threatenes to murder Killer Frost/Caitlin to force Cisco to help him with his weapon to destroy the multiverses. In order to save Catilin, Cisco agrees. When Savitar begins to intact his revenge Cisco brings the cure to Killer Frost, throwing it down at her feet. She is visibly moved. Killer Frost is unable to watch Cisco be killed, her feelings for Cisco which make her turn against Savitar. They stand together. United.
During HR's funeral, Caitlin appears hovering around at a distance. Cisco, Julian and Barry go over to her. She returns the cure and says she has become something else. She needs to figure it out. Cisco is relieved to see her but also accepting of her needing to figure out her own journey.
In the premiere, Cisco goes looking for Caitlin. He finds her working in a bar. The two banter and he tries to convince her to come back home. Cisco's words penetrate because later Caitlin returns ready to join Team Flash again. Much to Cisco's delight. The episode ends with Caitlin repeating Cisco's words, "We back baby." A sweet exchange betweent the two. Showing their bond always prevails. Throughout the season, Cisco supports Caitlin as she grapples with her dual identity as Caitlin Snow and Killer Frost. Often having to evoke her alter ego out with memories that Caitlin doesn't find pleasant, e.g. high school bullies. This once again shows the deep connection they have and how well they know each other.
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Caitlin and Cisco are working together on a cure for metas.
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Fans of the ship range from those enjoying their friendship, to those wanting them to be in a romantic relationship. Overall their relationship is enjoyed by most fans of The Flash.
On AO3, KillerVibe is the fourth most written relationship for Cisco and the second most written for Caitlin.
- cait x cisco tag on Tumblr
- cisco x caitlin tag on Tumblr
- killervibe tag on Tumblr
- snowvibe tag on Tumblr
- Both Carlos Valdes (Cisco Ramon) and Danielle Panabaker (Caitlin Snow) love their characters' relationship and consider them brother and sister
Notes and references
|SHIPS||slash||Coldflash • ColdRay • Coldwave • Hartmon • Olivarry|
|femslash||Agent Frost • Batfrost • Caitlicity|
Frostdrake • Smoakwest • Supersnow • Westpark
|het||Barricity • Cynco • Goldenvibe • Hawkvibe • Irisco • Killervibe • Laurisco|
Quickwest • Smoakvibe • Snowatom • Snowbarry • SnowStorm
SuperFlash • Supervibe • Theallen • Westallen • Westhawne
|CHARACTERS||female||Caitlin Snow • Iris West|
|male||Barry Allen • Cisco Ramon • Mick Rory|