This is probably my biggest fantasy. I'm into both */f and *m tickling, so seeing a man and a woman bound alongside one another and tickled fills both desires at once. Sadly, it's a rarity.
And for some reason it makes it all the better the closer and more intimate the relationship between the two. Random strangers is fine, but married is probably best, dating or longtime friends or siblings is great, too.
There are just so many interesting ways the scenario can be played out, depending on the scenario and if it's consensual or (fictionally) non-consensual. Maybe one person gives up information on how to best tickle the other, either to save themselves from more tickling or just because they secretly like watching their partner be tickled. Maybe one partner is broken (or rewarded) and then released so they can assist their captor in torturing the other. So many great options for this kind of scene.