Rashomon is one of my favorite movies, and it has several different themes worth exploring which are cross-genre. Here are a few tips to consider -
Have the focus of the adventure involve multiple, self serving participants. In the movie, you had observers who are also participants (one way or the other), but not only that. Most benefited (except maybe for the bandit, though for him, pride was at stake) from their observation being accepted as the truth. Make sure the benefit is also appropriate to the character.
Have each participant be from a distinct background, class and level of trustworthiness - and invert some of them. For example, in a fantasy setting, a LG party may sympathize with the views of a Paladin. Make that Paladin a liar, but caught in a lie that meets alignment standards (ie a lie to protect a virtuous lord).
Keep the cast of NPCs six or below. You don't want to lose attention of your players, or, have them mix up details.
Have severe consequences. So if the warrior is found guilty, he gets a room, TV and a phone call? Being found guilty of the incident, death awaits.
May there Always Be Doubt. In the film, the viewer sees through the eyes of the judge. There should never be a slam dunk, and you should avoid allowing spells that allow too much of an advantage. If your version of "speak with dead" includes some manner of truth testing, get rid of it. "Detect Lie" should never be available.
I'd want my players to feel they made the best possible choice in the end, but still have a nagging doubt or two which leaves open the opportunity of a sequel. The setting of Rashomon, a mostly divided, war torn Japan, a land with no ultimate "source of good" mythology, adds to the mood of the film, but that isn't a theme relegated to Japan. A modern setting could involve a UN investigative team going into a war torn region to investigate atrocities.
