I want to run a Rashomon style session soon and I'm looking for solid advice, as well as lessons learned from your own experience doing so.
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.
My advice is: bring a hat.
I just remember reading something about using rakugo style props, as a GM. I think it was in Instant GM, a bag of tricks.
So the players are going to see a story unfold, or interact with different characters who saw a story unfold who each have their own point of view. In order to easily make the NPCs stand out, just wear the hat differently. As a peasant, take the hat off and hold it in front of you in the presence of these great heroes. As a warrior, wear the hat low on your brow, and look down at the players. A travelling entertainer: wear it off to the side, at a jaunty angle. A noble lady: fold it up and use it as a fan or kerchief in front of your face. That kind of thing.
Actually I don't think a hat is a traditional rakugo prop, but hopefully you get what I mean.
Oh that's a nice game structure. I did not have the chance to arrange such a game, but there's another movie I strongly suggest you to watch : Hero. It's a chinese wuxia movie, with intense artistic colors and an incredibly poetic "point of view" plot.
Another important movie to watch to get ideas from is 12 angry men, an impressive dramatic movie about a jury and a trial for murder.
I think you can organize your plot as follow. Let the characters talk first with the dead (as happens in Rashomon) preferably through a NPC cleric with "speak with dead", but a better choice would be to have a PC as a ghost, and have him join other living characters to find his assassin. His point of view is apparently more authoritative, because he is the one directly involved in the killing, but his authoritativeness is plagued with resentment, which lead to put too much stress on useless facts. It's clearly an investigative plot, they will have to interpret a lot of details.
If your adventure is going to use D&D 3.5, remember that the ghost character requires the archetype system, which introduces additional complexity, hence the ghost character must be interpreted by an experienced player. Also note that the level advancement is different, due to the additional skills a ghost possess. In such investigative adventures, the characters are not supposed to level up a lot.
Point of view can not only be observation of a direct event, but also "different destiny", or "different interpretation of the past". Example: suppose your PC find a gem which shows things from a different point of view. The point of view changes according to the influence that each PC character's past would put in the observed object, person or event. Kairin, a PC rogue with a troublesome past, observes a Pelor priest through the gem, and sees a violent thief. The petty criminal past of the priest childhood is exposed, but grossly exaggerated by the intrinsic roguish point of view of Kairin. Panyar, a PC paladin will observe the same priest through the gem to see a good man, full of compassion and kindness.