No, Barry Allen doesn't date Caitlin Snow in the comics. Their relationship is mainly professional and based on working together as members of the superhero team.
Well, without more context, it's hard to say exactly. However, if we assume the '278' doesn't hold a super - specific meaning, a Killer Frost fanfic might focus on her transformation. It could show how she became Killer Frost, the internal struggles she faces, like dealing with her new identity and the powers that come with it. It might also involve her interactions with heroes or villains, and how she navigates the world of the DC Comics.
In the comics, Killer Frost's death varies depending on the specific storyline. Sometimes it's due to a powerful enemy or a self-sacrifice to save others.
A plot could revolve around Caitlin and Barry being forced to work undercover as a couple to infiltrate a criminal organization. As they pretend to be in love, they start to realize their true feelings for each other. Or perhaps Caitlin's scientific knowledge and Barry's speed are the only things that can stop a city - wide disaster caused by a malfunctioning S.T.A.R. Labs experiment.
One great 'Batman x Killer Frost Fanfiction' is 'Frosty Encounters'. It has an interesting plot where Killer Frost is forced to team up with Batman against a common enemy. The author does a great job of exploring their dynamic, with Batman being his brooding self and Killer Frost having her cold and snarky attitude.
I'm not sure where you can specifically find 'killer frost 278 fanfic'. You could try searching on popular fanfic websites like Archive of Our Own or FanFiction.net. Just type in 'killer frost 278' in the search bar and see if it shows up.
One unique way to develop their relationship is to put them in a situation where they have to swap powers for a short time. Barry would have to deal with Caitlin's cold powers and Killer Frost side, while Caitlin would experience the speed force. This would make them understand each other better and deepen their connection. Also, they could be trapped in a time - loop together. Repeating the same day over and over would force them to rely on each other in new ways and explore their feelings more deeply.
I recommend the novel "The Killer's Beautiful Wife's Powerful Return" to you. This is a modern romance novel written by the author, Fu 'er. Although it did not completely match the given character name, there was also a killer called Snow White in this novel. The novel described the assassin who had been betrayed and died in his previous life. After being reborn, he used his superpower and assassin skills to play tricks and was unwilling to be betrayed again. I hope you like this fairy's recommendation. Muah ~😗