Stockholm Syndrome is not really a "trope"—not in the sense this site usually uses the term, anyways. It's not a story element with a distinctive shape. It's a very slippery term that gets applied to all sorts of quite disparate things. (Sort of like Mary Sue.) For example, two inverse meanings of the term are:

• An initially kidnapping relationships that turn caring (A Match Made in Stockholm)
• An initially caring relationships that turn abusive and/or controlling (Domestic Abuse)

One possible interpretation would be that Stockholm Syndrome is a heavily misused trope. I think that would be a difficult to maintain, though. If Stockholm Syndrome were to be distilled into a "real" trope—something that's cohesive and distinctive—that would require cutting out a significant portion of how the term is actually used in practice (not just on this website, but in popular discourse in general). Trying to define a trope in a way that differs from the common understanding of that term is a recipe for misuse.

Since it's functionally impossible to re-define an established term, and since the term's common usage is too broad for a single trope, I propose that Stockholm Syndrome be turned into a Definition Only Page.

Most of these could be recategorized as platonic A Match Made in Stockholm — platonic is included in the definition, albeit as a footnote (and I think most people don't know that, since the name doesn't really suggest so). But I think people's common understanding of tropes often draws a distinction there.

1. Vikings: Athelstan's respect and affection for Ragnar's family grows over time in spite of the fact that Ragnar violently enslaved him. However, part of the reason Athelstan sticks around is because Ragnar treats him well and he has nowhere else to go. By Season 2, he feels like a part of the family, and Ragnar's family feels the same way.
2. Alpha Dog: Zack's response is a combination of this and not taking the situation seriously. He's beaten up, kidnapped, tied up and gagged. And yet he shows absolutely no ill will towards his captors. He ends up having a great time with them, and freely offers to claim he ran away to keep them from getting in trouble. This is based on reports that the real Nicholas Markowitz was often seen in public with the people who kidnapped him, and apparently made no real effort to escape.
3. Panna a netvor: Though she is basically a hostage, Julie starts to fraternize with Netvor because he treats her well, and out of boredom and loneliness.
4. Pour cent briques, t'as plus rien...: The hostages sympathize with Sam and Paul, even more so when Sam offers to share the loot with them.
5. The Princess Bride: Westley's ship was taken by the Dread Pirate Roberts, who famously leaves no survivors. Yet Roberts spared Westley, keeping him around, each night saying, "Good night, Westley. Good work. Sleep well. I'll most likely kill you in the morning." In the meantime, Westley was able to learn swordplay, fighting, and anything else the pirate crew would teach him. Eventually, Roberts, who had clearly taken a liking to him (Lima Syndrome), revealed the secret behind his title to him, and later Passed the Torch to Westley.
6. 20,000 Leagues Under the Sea Professor Arronax gradually becomes more impressed with Nemo during his stay onboard the Nautilus. Ned Land is the only one who seems to remember that they are prisoners, not guests. It's only when Nemo launches another attack on British vessels that Arronax remembers this too.
7. Eigen Kweek: Bernard, the henchman of "Den Hollander", develops this for Julita as they bond over their respective families. He eventually ends up romantically involved with Julita's sister, Nenita. Julita and Bernard do end up becoming good friends (and even in-laws), despite the entire kidnapping situation.
   Ria [to Julita]: Is it true? Are you "sick from Stockholm"?
8. Malcolm in the Middle: Reese lets a bunch of thugs into his house for a "party," where they end up running what is strongly implied to be some kind of meth lab. For the whole weekend. Naturally, Reese ends up admiring them.
   Malcolm: Don't you know about Stockholm Syndrome? You're starting to identify with your captors.
   Reese: My captors?! These guys saved my life, man!
   Malcolm: Only because they decided not to kill you!
   Reese: Same thing.
9. Star Trek: The Next Generation: In the episode "The High Ground," Capt. Picard is kidnapped by terrorists and brought to Dr. Crusher who was kidnapped earlier. As they are conversing, Crusher admits that she's been talking to the leader and beginning to understand his point of view, and Picard reminds her of the psychological implications of being a hostage, which obviously refers to stockholm syndrome.
10. The Last Kingdom: How else to explain Uhtred's affinity for the Vikings who invaded his homeland and slew his father and brother in battle. Granted, Ragnar saves him from his Evil Uncle Ælfric and eventually considers him Like a Son to Me, but still...
11. You (2018): Will genuinely likes Joe as the episodes go on, not informing the cops even though he had every opportunity to do so. He even sends Joe postcards from Manila and gives him advice after he's been set free.
    Joe's monologue: Joe: Oh! See that? Living proof. I have let people out of the cage, made friends, even, from the experience.

1. Dark Souls: Legends of the Flame: At least one of the warriors that were petrified by the spider lady came to fall in love with her.
2. Cry Blood, Apache: Apache woman Jemme is abducted by the gang who murdered her tribe, as they believe she can lead them to gold. Over the course of her ordeal she falls in love Pitcalin, the only one of her captors to treat her with kindness.
3. In The Phantom of the Opera, decades before the Stockholm bank robbery occurred, Christine falls in love with Erik after he kidnaps her, drugs her, and locks her in his house for two weeks — all this after three months of him as an Unseen Pen Pal and gradually growing more verbally abusive and aggressive. Raoul is saddened but not the least bit surprised that she loves a man she's (understandably) terrified of, and Christine comes to her senses long enough to tell Raoul to take her away from Erik once and for all No Matter How Much I Beg.
4. The Orphan Master's Son: Discussed by Dear Leader and Commander Ga. Dear Leader wonders if his American captive is falling in love with him.
5. The Reynard Cycle: Though she doesn't exactly love him in the traditional sense, this trope explains how the Countess Persephone and Duke Nobel ended up in what would generally be considered a fairly healthy marriage. A captive of war, her original quarters in the palace were essentially a Gilded Cage. By The Baron of Maleperduys, she actually has to be reminded that he was the man who (indirectly) killed her father.
6. The Sevenwaters Trilogy: Liadan falls in love with the leader of the mercenaries who kidnap her. The reverse is also true, with apparently the entire crew experiencing Lima Syndrome.
7. The Sheik: ZCE but both A Match Made in Stockholm and Stockholm Syndrome are both listed
8. The True History of the Conquest of Mexico: After Tenochtitlan is taken, Cortés allows for the Mexicas to recover the female hostages the Spaniards had been taking. The problem, it turns out, is that most of those women have already hooked up with Spanish soldiers and are now Christian, married, pregnant or some combination of them, so they refuse to return to their own people. At the end, out of a contingent of possibly more than a hundred of women, only three of them return.
9. Snowdrop (2021): Bun-ok is this to Joo Gyeok-chan, one of the North's spies who taken her and the dormitory residents as hostages, due to his fierceness. In return, Gyeok-chan also felt the same way to Bun-ok.

These are basically "kid views people-who-are-effectively-their-adoptive-parents as adoptive parents", but the adoption was kind of kidnap-y.

1. In Island of the Aunts, there is a mild case - the titular aunts kindnap children who are unhappy in their normal lives, anyway, and take them to a magical island. The kids initially want to get away, but after some time they find that the aunts are better parental figures than their actual parents, and help the aunts fight off the villains (who might have rescued them, but would also kill the magical creatures living on the island).
2. A Song of Ice and Fire: Theon has some of this for the Starks. Theon was taken hostage by Ned Stark because his father lost his Rebellion and isn't allowed to go home until his father (and probably his mother) are dead. He takes it in stride and becomes friends with Robb, but only comes to terms with the reality of his situation when he finally gets to return home.
3. The Folk of the Air: Jude and Taryn have grown to love Madoc like a father while resenting him for killing their parents at the same time.
4. Raised by Wolves (2020):
   • The Mithraic children are essentially taken prisoner by Mother and Father, but they all eventually prefer the androids to their own people, even though most do not abandon their faith.
   • Once Paul discovers that Caleb and Sue are actually imposters who killed his original family, he eventually decides to treat them like his parents anyway. He seems to forget about it occasionally, such as when he requests that Sue sing a lullaby to him like she used to, and Sue has to remind him that that wasn't her.
5. Los Protegidos: what most of the kidnapped children are going through. They call their kidnappers "Padre" (Father) and "Madre" (Mother).

1. Flowers in the Attic has a moment where Chris rapes Cathy in a fit of desperation. Afterwards she says she could have stopped him if she wanted to, and they end up beginning a full blown incestuous relationship in subsequent books.
2. The Girl on the Train: Anna at the end; even when Tom is revealed as a violent, cheating, misogynist murderer still sides with him over Rachel - or she pretends to, then slips away to call the police and an ambulance, before finishing Tom off with a corkscrew Rachel hit him with earlier.
3. Interview with the Vampire (2022): Discussed Trope. Daniel calls it "Classic Stockholm" when Louis (the abused) is still in love with Lestat (the abuser) after barely surviving a horrific physical assault. Lestat is a controlling boyfriend, but not a kidnapper.
4. You (2018): Implied to be the case with Joe and Mr. Mooney, who took Joe in from foster care in the latter part of his youth. Joe genuinely cares for and admires the old man, despite his upbringing including verbal abuse, slaps to the face, and being locked in a cage for days on end. That said, he does refer to Mooney as "a Soviet prison guard," so he's not completely clueless about how badly he was treated.

1. Samurai 7: Rikichi's wife with Ukyo's predecessor, aided by the fact that she's been impregnated with his child. By the time Kambei arrives to rescue her she doesn't want to be rescued.
2. Michiko & Hatchin: In a more cynical view, this might be what causes Hatchin to bond with Michiko. Then again, anything would have been better than Hatchin's life with her foster family.
3. Hell Girl: The only believable reason Yumi still seeks her father's approval and puts all the blame on Yuki instead.
4. GUN×SWORD: Michael.
5. Blue Literature: Arguably, Shigemaru's youngest wife seems to have developed it towards Shigemaru and Akiko.
6. The Seventh Bride: A tragic case with Ingeth.
7. Dr. Franklin's Island: Referred to in all but name. Semi and Miranda, particularly Miranda, have difficulty with this.
8. Dexter: Emily Birch for Jordan Chase in Season 5.
9. Der Tatortreiniger: Come on, who couldn't sympathise with the cold-blooded axe-murderer from Über den Wolken? Schotty certainly could.
10. Tamburlaine: Zenocrete.
11. Neonomicon: Elements of this come into play in the scene where Brears talks to her One rapist.
12. Strontium Dog: King Clarkie actually enjoys being kidnapped by mutant rebels, he spends most of the time identifying new species of insect. Enjoying? Does that mean bonding with? It's not clear.
13. Path of the King: Horribly invoked with Yukiko via Rule of Blood.
14. Never Say Never Again: "She could have turned."
15. Subject Two: Arguably happens to Adam toward Dr. Vick during their experiments.
16. The Wind and the Lion: The Raisuli kidnaps the Pedicaris family, slaughtering their servants and friends in the process, and yet the whole family decides to risk their life rescuing him by the end. Mind you, the kids think being kidnapped by desert raiders is the best thing ever from the beginning.
17. Broken Love Series: One explanation for Lake's feelings for Keiran, other than him being hot like burning.

1. It's Always Sunny in Philadelphia: Referenced in "The Gang Gets Held Hostage," when most of the gang mistakenly believe that it's a physical illness.
   Mac: Oh my god, he's burning up! Clearly Charlie is coming down with a nasty case of Stockholm Syndrome!
2. The Fable of the Dragon-Tyrant: After centuries of submitting to the horror of the dragon, people have come to accept it as a necessary and beautiful part of life. Anyone showing this mentality towards anything else will get ridiculed, and yet, in reality, this attitude is the confusing norm.
3. Maid Marian and Her Merry Men: King John's torture victims are horrified by the idea of leaving the torture chamber and going to live in the world with all its stress and fast carts and modern technology (like pointy sticks).
4. Bomb Queen: Despite almost everyone suffering from the lawless nature of New Port City - whether it is the death or abuse (physically and sexually) of themselves and their loved ones from Bomb Queen and all of the criminals that thrive there - Bomb Queen and her anarcho-authoritarian hold on the city has an overwhelmingly positive approval rating, with every man, woman and child there willing to fight for the status quo the city is under.