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Incest between sisters. No brothers allowed.

Siscest is between a specific set of sisters. Twins (Identical or Fraternal), full, half, & three-quarter (horizontal or vertical). Sisters that are excluded step, foster, and adoptive.
Our successful siscest relationship has flourished greatly due to the lack of parents.

Notice: siscest sounds like success.

The best incest is siscest, wincest.

Keep up the siscest you two, you'll have a future in Hollywood.
by a super secret moose January 16, 2017
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