Specifying a pairing was what aralias originally asked for, and once I'd started tinkering I began to think "It wouldn't be much of a stretch to add this or that feature while I'm here..."

Of course, even when you force a pairing on it, it doesn't necessarily get the people the 'right' way round :-) For example, prompt 237 with Kirk and Spock (or Jamie and Zoe, or Tegan and Nyssa) works beautifully one way round, and not at all the other.

Ace and Dayna's exploding wedding night, on the other hand, seems about the same whoever's who.