Basic Trope: A romantic and/or sexual relationship between twins.
- Straight: Half-Identical Twins Alice and Bob are lovers.
- Exaggerated:
- The story takes place in a Deliberate Values Dissonance culture that believes twins to be reincarnated lovers. It's completely accepted—even expected—of twins to fall in love.
- Alice and Bob regularly have threesome sex with their other triplet (or quadruplet) sibling/s.
- 'Logical Extreme Alice and Bob are a part of an Octuplet Harem.
- Downplayed: Alice has a crush on her twin brother Bob. He doesn't like her back.
- Justified:
- As twins, Alice and Bob are considered to be born married by their culture.
- Alice and Bob are reincarnated lovers who happened to end up in the same mother's womb.
- Alice and Bob are long lost twins who were Separated at Birth and fell in love not knowing they are related. Genetic Sexual Attraction may be involved.
- Childhood Friend Romance and First Girl Wins
- Alice and Bob are Human Aliens whose species isn't given to major genetic diseases, and so lack an incest taboo or anything like the Westermarck Effect. Due to their close bond, this behaviour is considered normal in twins of their species.
- Inverted: Their family practices Royal Inbreeding, or they are part of a Breeding Cult. Alice and Bob are supposed to get together—but they refuse.
- Subverted: Alice and Bob do have some initial chemistry—but luckily Charlie appears, and the real romance between Alice and Charlie starts (a la Star Wars).
- Double Subverted: It turns out Charlie is their long-lost triplet!
- Parodied: Quintuplets are in a polygamous marriage.
- Zig-Zagged: Alice and Bob are twins caught in endless Will They or Won't They?.
- Averted:
- There is no romantic or sexual relationships between twins.
- There are no romantic or sexual relationships at all.
- There are no twins.
- Enforced: Characters all look like twins.
- Lampshaded: "How could I not love you? We were together from the beginning, since we came from the same womb."
- Invoked: An Incest Yay Shipper on Deck plays The Matchmaker for Alice and Bob.
- Exploited: A Clingy Jealous Girl is pursuing Bob. He alerts her to the fact that his sister Alice is his incestuous lover to creep her out so she'll leave him alone.
- Defied:
- Alice and Bob don't act on their mutual attraction.
- Alice and Bob have UST, and so other people keep them apart to make sure they don't become lovers.
- Discussed: "Bob and Alice seem to be awfully intimate with each other, even for twins. Do you think they're like… together?"
- Conversed: "Beautiful twins in a porno movie. This can only lead to twincest."
- Implied:
- Deconstructed :
- Alice becomes pregnant with Bob, and her child is born heavily deformed due to inbreeding.
- Everyone around Bob and Alice are repulsed by their relationship and they meet with constant prejudice and discrimination.
- Reconstructed :
- Bob and Alice get counseling to overcome their... less than healthy affection towards each other.
- Bob and Alice decide they don't want children at all.
- Alice and Bob adopt a child.
- It isn't impossible for Alice and Bob to have healthy biological children, merely meaning they have to be more careful to prevent their negative recessive genes from becoming expressed.
- The twins in question are of the same sex—getting each other pregnant isn't even possible.
- Alice and Bob are fiercely protective of their child, and will fight anyone who suggests that being disabled means their kid's life doesn't have value.
- To escape scrutiny, Bob and Alice run away and start a new life under fake identities, and pretend they're just Lookalike Lovers.
- Played For Laughs:
- Alice and Bob are part of a crazy, royal/wealthy, inbred family and it's treated like a throwaway joke.
- Alice and Bob appear in a Soap Within a Show just to illustrate how weird it is.
- Played For Drama: Alice and Bob, already doing most things together, primarily become an incestuous couple not because of romantic love—but because nobody considered the consequences of deliberately making them extremely bonded. Thus one of the things they angst about the most is how their relationship only exists because of how played up their twin status was.
I mean, you could go back to Twincest, but it's like the twin page of this page! That's so wrong!
