: A romantic, possibly sexual relationship between siblings, or half siblings related by blood.
- Straight: Bob and Alice are very much in love and secretly hide their affection to avoid scorn from their peers.
- Bob and Alice were in a relationship before they even knew they were related.
- Alternatively, Bob and Alice are twins, and are considered to be born married by their culture.
- Bob and Alice are villains that don't care about right or wrong (or are doing it precisely because it is "wrong").
- Or they're creepy and unaware of the implications of Brother-Sister Incest
- Or one of them is an adopted sibling, and they think that since they aren't really related it's okay.
- Bob and Alice are in place and time where incest isn't taboo, their parents may even encourage it to keep their bloodline "pure". (according to the Royal Blood notion)
- Alice and Bob decided that it would be for the best if they ended their relationship and saw other people because incest is 'unnatural.'
- Not Blood Siblings
- Doubly Subverted:
- Parodied: The siblings' parents make a wager to see how long it will take for Bob to get into Alice's pants.
- Zig Zagged: Their parents find out about their relationship and are horrified, separating Alice and Bob so they can never be together. During which time one or both of them painfully learn to let go of their love which apparently was not meant to be. Only to eventually meet later in life where their feelings are immediately rekindled.
- Bob does not have a sister.
- Bob's sister dies a long time ago.
- Bob does have a sister, but they have a normal relationship.
- The author fantasizes about that.
- The author is using incest as a plot point to create drama between Alice and Bob.
- The author is using incest to make a point about society.
- It's based-on-history work, about culture that Brother Sister Incest is common. It's nothing more than the author show that he did some research.
- Lampshaded: "I know society will never accept us...but I don't care..."
- Exploited: Bob is a corporate CEO, and his competitor, John, lets the story loose, intending to ruin Bob and remove his competition.
- Defied: Alice rejects Bob's advances.
- Discussed: "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!"
- 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 mental retardation and genetic diseases.
- Or, alternatively, this is presented as completely normal.
- 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 Doctor informs them that their baby is unhealthy because it was born prematurely, and that inbreeding had no factor.
- The baby manages to overcome their short comings as they grow older, proving that they were not as unhealthy as feared.
- 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.
You can go back to Brother-Sister Incest
if you like, but...seriously, that's just wrong