For starting out as bitter enemies, Buffy and Spike became one of Buffy the Vampire Slayer's most celebrated couples. Despite being asked dozens of time if Spike was her boyfriend throughout the series, the Slayer vehemently denied the chemistry she had with viewers' favorite bleach-blond bad boy. Their story wasn't all about sexual tension you could cut with a battleaxe; the intimacy between their characters only deepened as they went through — and overcame — each new crisis.
From battling each other to battling side by side, every season revealed a little more about their powerful dynamic. The writing of these particular episodes explored the many facets of their relationship development, and were important because of how the unique interactions between Buffy and Spike brought out distinct sides of their characters.
"Something Blue"
An amusing fan-favorite episode from Season 4, in which a frustrated Willow starts enacting renegade magic. She becomes so irritated by Buffy and Spike's behavior that she accidentally spits out, "Then why don't you marry him!", thus beginning an arc where Spuffy (at least in pretense) begins.
Willow causes mayhem to other characters, too, but fans couldn't get enough of the spell that brought the Slayer and the vampire she loathed most together, and loved their flurry of make-out sessions that predate their first "official" kiss, all of which causes Giles to feverishly cleaning his glasses.
"Out of Mind"
In one of the earliest episodes of Season 5, Spike has a shocking revelation in a passion-fueled dream — he's in love with his sworn enemy. At the time, he'd been assisting the Slayer and her super soldier boyfriend Riley with slaying in the cemetery.
In Spike's dream, Buffy seeks Spike in his crypt with the intent to slay him. He welcomes death, declaring he'd rather die and be free of her. She's naturally confused by this, but can't bring herself to kill him, which is when they share a fiery embrace, and Spike wakes up horrified.
"Crush"
A distraught and frustrated Spike tries to coerce Buffy's affections by kidnapping her along with his former lover Drusilla, hoping that Buffy will finally see how devoted he is to her by staking his sire (as if the shrine she found of herself in his crypt wasn't enough). When his love appears not to be reciprocated, he threatens to release Drusilla and have her kill Buffy instead.
The mid-season episode is notable for not only the climactic confrontation between Spike, Dru, and Buffy, but because it ends with Spike's invitation into Buffy's house being revoked. It begins one of many character arcs for Spike involving regaining his crush's trust and proving that he loves her in a meaningful way.
"Intervention"
In this popular Season 5 episode, hell goddess Glory is searching for the mysterious "Key" and thinking it's in the possession of whomever the Slayer holds dear, kidnaps Spike. Meanwhile, Spike has enlisted Warren's help in making him a "Buffybot," a perfect android replica of the Slayer, whom he's fallen in love with.
The real Buffy despises Spike for both creating the repugnant Buffybot and potentially revealing Dawn's location, but ends it being in his debt because despite being tortured, Spike never revealed the whereabouts of the Key, keeping Dawn out of harm's way. Posing as the Buffybot, the real Buffy bestows a kiss (and her trust) on her knight errant.
"Once More With Feeling"
The groundbreaking musical episode in Season 6, which has since inspired countless imitations across many genre series, features beautiful ballads from the entire cast, but perhaps none as meaningful as the ones exchanged by Spike and Buffy.
After Dawn releases a demon who makes everyone unable to stop dancing and singing, Spike reveals to Buffy how tormented he is being in love with her, and she reveals how painful it is to have been pulled from heaven. They realize they're two lost souls that might be able to find happiness (or at least feelings worth living for) in each other, and they share their first "real" kiss at the end of the episode.
"Tabula Rasa"
A fan favorite across the entire series, this early Season 6 episode explores what happens to the Scoobie when one of Willow's spells goes wrong and robs them of their memories. Their process of piecing together their personal histories makes for some hysterical role reversals.
Not knowing their history both improves and complicates Buffy and Spike's relationship, especially in lieu of the kiss they shared at the end of "Once More With Feeling." When the spell eventually is broken and they encounter each other at the Bronze, they resume their passionate affair.
"Smashed"
With the sexual tension building in several previous episodes, it finally erupts in the middle of Season 6, when two unstoppable forces collide to quite literally bring down the house. Spike and Buffy get physically intimate for the first time, and the episode proves their relationship will be very different than what she had with Angel.
Buffy and Spike's lovemaking is violent, demanding, and destructive, and causes a house to collapse. They aren't concerned with the ramifications of their animal passions, which sets the tone for their affair, which Buffy conceals from her friends out of shame.
"Beneath You"
Spike makes a powerful choice at the end of Season 6 to leave Sunnydale and travel to Africa, where he hopes to be given his soul, much like Angel was. When he returns to Sunnydale in Season 7, the process has left him weak and damaged, both mentally and physically, to the point where he feeds on rats under Sunnydale High where Buffy has taken a job as a counselor.
At the end of the episode, when Buffy encounters him in a church speaking in riddles, she realizes that the broken man before her has a soul, one he acquired to make himself the kind of man she would want, forgive, and love.
"Touched"
Season 7 of Buffy the Vampire Slayer was light on the romantic intimacy between Buffy and Spike, but what it lacked in steamy kisses and sexual tension it made up for in deeper understanding between the characters. In "Touched," towards the end of the season, Spike has a frank conversation with the Slayer when she's feeling depressed.
In his speech, he explains that his love for her isn't because he "wants her" or even because he "can't have her," but because he loves who she is. He's seen her at her best and her worst, and he truly believes she's "one hell of a woman." For all her strength and resilience, she demonstrates incredible vulnerability with Spike when he's finished and they share a chaste yet intimate night together.
"Chosen"
The series finale of Buffy the Vampire Slayer is meaningful for a variety of reasons, but one of the most salient events of the episode concerns Spike and Buffy, a pair whose kinetic connection wasn't always healthy but always undeniable.
They had gone through so much in the preceding seasons, and their relationship had changed to an extent that fans believed they might have had a future together when Spike decides to sacrifice himself to save his true love. Buffy finally tells Spike she loves him, and he dies the man who deserves it.