Basic Trope: A romantic and/or sexual relationship between siblings or half-siblings.
- Straight: Siblings Alice and Bob are very much in love and keep their relationship secret.
- Exaggerated:
- Alice is in a Sibling Triangle with her two brothers.
- Alice is in a relationship with her twin brother, Bob.
- Downplayed:
- Bob and Alice are dating, but don't sleep with each other.
- Bob and Alice are half-siblings and thus, don't consider it to be "that bad".
- Bob and Alice are Flirty Step Siblings.
- Bob and Alice are Not Blood Siblings.
- Alice turns down Bob's advances for reason other than their familial relationship.
- Justified:
- Alice and Bob were in a relationship before they even knew they were related.
- Alice and Bob are villains that don't care about right or wrong (or are doing it precisely because it is "wrong").
- Alice and Bob are in setting where incest isn't taboo—their parents even encourage it to keep their bloodline "pure".
- One of them is an adopted sibling, and they think that since they aren't really related it's okay.
- Childhood Friend Romance and First Girl Wins
- Inverted:
- Alice and Bob hate each other—far more than simple sibling rivalry—and are trying to kill each other.
- Alice and Bob are completely apathetic toward each other, with no passionate feeling of any nature.
- Subverted:
- Dana claims Alice and Bob sleep together, but the viewer later learns that she's just spreading nasty rumors about them as slander.
- Alice and Bob aren't siblings; people only think they are because of a misunderstanding.
- Double Subverted:
- Dana might be trying to hurt Alice and Bob with the rumors, but that doesn't mean she made it up...
- Dana did make up and spread nasty rumors that Bob and Alice were incestuous—how was she to know it was true?
- Parodied:
- Their parents make a wager to see how long it will take for Bob to get into Alice's pants.
- Alice and Bob date, and when they break up Alice begins dating Charlie and Bob begins dating Diana. Who are also Alice and Bob's siblings.
- Just being told they're siblings instantly make Alice and Bob fall in love, despite having had no idea who the other was mere seconds ago.
- Zig Zagged: Alice and Bob are siblings caught in endless Will They or Won't They?.
- Averted:
- Alice is an only child.
- Alice does have a brother, but they have a normal relationship.
- Enforced: It's based-on-history work, about culture that Brother Sister Incest was common in. It's nothing more than the author show that he did some research, though in interviews he admits that he finds it weird and would rather have not included it.
- Lampshaded:Bob: I know society will never accept us, but I don't care.
- Invoked:
- Alice was born so that she would marry Bob and continue the family bloodline.
- It's creation tale, with Adam and Eve Plot, and they're only two humans/deities exist at that point.
- Exploited:
- Bob is a corporate CEO, and his competitor, Dana, lets the story loose, intending to ruin Bob and remove her competition.
- Dana uses her knowledge to blackmail Bob into merging their companies together.
- Defied: Bob flirts with his sister Alice, but she rejects Bob's advances.
- Implied: Incest Subtext
- Discussed:Alice: Bob, this is wrong... we're brother and sister... nobody will ever understand...
- Conversed: "That's disgusting. I can't believe that sicko Bob is doing... that to his sister. His sister!"
- Deconstructed:
- Society conditionally won't accept Alice and Bob's love, driving both into a deep depression from the constant harassment they receive just because they're together, ruining the happiness in their relationship.
- Alice becomes pregnant, and the baby exhibits all the health problems associated with inbreeding, such as intellectual disability and genetic diseases.
- Reconstructed:
- Alice and Bob get counseling to overcome their... less than healthy affection towards each other.
- Alice and Bob decided to move far away, where the society that couldn't accept them can no longer hurt them. And lead a happy life together.
- The baby manages to overcome their short comings as they grow older, proving that they were not as unhealthy as feared. Alice and Bob are also Mama Bear and Papa Bear and will fight anyone who says being disabled means their kid's life isn't valuable.
- Neither of them ever wanted to be a parent, so they just don't have children.
- Or if they want to be parents, they decide to adopt.
- Played For Laughs:
- Bob and Alice's parents grill him just like all of Alice's new boyfriends.
- Bob's friends don't know that Alice is his sister and attempt to be a Shipper on Deck for them, much to their horror.
- Played For Drama:
- Alice and Bob's story is told through a combination of Sympathetic P.O.V. and non-sympathetic POVs. Sometimes it seems like Alice and Bob are Star-Crossed Lovers, and other times it's just Squick, leading to a complex and angsty story.
- Bob and Alice aren't the least bit bothered by their relationship or even the mere fact that they're attracted to each other because they grew up in a pretty messed up family that taught them that such a thing was normal.
- As disturbing as their relationship is, it's Bob and Alice's way of dealing with shared trauma since they could only find comfort in each other. Had their circumstances been different, they would've had a normal sibling relationship.
- Alice sexually abused Bob since childhood (or vice versa).
You can go back to Brother–Sister Incest if you like, but... seriously, that's just wrong...
