The only similar story I've heard of had the main character remain delusional, he was told to kill civilians by his commander, and then he attempted to get revenge on the commander for being a traitor.
The story used two psychological facts.
Second: Being a fps game, the players automatically believe in taking orders, shooting everyone, and the exciting plot twist of betrayal. That's how they usually work.
I can't really do that. This has to be the player's choice. It isn't about morality and authority, it's about intrinsic assumptions within the medium. I'll get to morality and authority later. (And in greater depth, since that's a subject for which I have plenty of bile to dispense.)
If you can avoid killing, you can only outright trick the people who don't think about it. But here are some ideas to unspolier the game.
- You may present some extrinsic reward system or a walkthrough that doesn't suggest any alternate path, so that players who rely on these things are less likely to find out the plot of the game accidentally.
- You will have to make sure that the player has to work harder to be good, no accidental mercy.
- No accidental killing either right? If you hand them a knife they might stab before they know what's going on like in Calm Time.
- To reduce the severity, you shouldn't actually show the killing until the end, if the player's annoyed enough they'll think about it.
1. There would be a "kills" tally. This would go with no explanation. I'm fairly sure most players will think it's a mark of status at first, but any player who's completed the game will realise this is a mark of shame. Especially since it allows more detail at the end of the game, where you can finally review all your stats, and when reviewed the kill tally gives you more detail. Such as a kill tally of 29 becoming "6 men following orders to protect a man they knew nothing about and wouldn't have helped otherwise, 5 men who never really stopped to consider what they were doing, 4 single men working overtime at a dead-end job they hated, 3 women who couldn't get any other work with their skill set that didn't involve nudity or burger flipping, 3 single fathers whose children are now in a system of constant abuse, 2 newlyweds who couldn't afford a honeymoon with their shitty security jobs, 2 gullible youngsters desperately struggling to believe they're the good guys, 2 security guards wondering if their shift was ever going to end, 1 man who was sympathetic before but sure thinks you're an asshole now and 1 total bastard who actually deserved it." That might be a bit anvilicious, though.
2. Well, they have to think. Less-lethal options are harder to use, and not as effective. (Just like in real life.) Finding a way around takes effort, and sometimes isn't an option. (Just like in real life.) Bribing and conversation are questionable at best and can't always be done, especially if the other side is just as delusional as the typical player. (Just like in real life.)
3. It's going to be pretty hard to kill somebody by accident. You will have whatever weapons you brought, so nobody is giving you weapons at any point, and in conversation they're always put away.
4. Come again?
Ok that's all I have for if you want it to work the first time.
On the other hand, you could alter the allowed perception so players think they're killing monsters. This is would be a lot like accidental killing. I watched a zombie-like movie, where an outtake suggested the virus altered body and perception of the infected to the extent that the "monsters" thought they were super humans and the real humans looked like horribly diseased and dying monsters who kept trying to grab at them.
I can't do that, it'd kill the game's message to overtly alter it like that. At the very least, I can say that people assume they're killing monsters in games anyway, even when those monsters are human beings. Usually, their justification is "Well, we're the good guys and they're the bad guys", or some variation thereof. That's a shitty excuse, and that being a shitty excuse is the whole point of the game.