The world has experienced a massive nuclear war. This was followed by a short but harsh nuclear winter and numerous pandemics. Some of the pandemics were caused by the release of biowarfare agents from damaged government labs. As a result, humanity was nearly eradicated. In urban areas there is perhaps one person left for every 100 square kilometers.

The world is now filled with the restless souls of the dead. The player roams the world, struggling to survive and attempting to put to rest as many ghosts as possible.

The survivors are usually pretty crazy. One of these biowarfare agents was a virus which could cause brain damage, resulting in survivors suffering permanent delusional beliefs, hallucinations, and amnesia.

The protagonist explores the world, trying to survive and put the ghosts to rest.

[This world was designed to be a total conversion mod for the video game Fallout 4.]

post-apocalyptic horror

Day/Night

Day time is scary and dangerous.

Night time is absolutely terrifying and extremely hazardous. The strength of the ghosts increases, and the number of them manifesting increase enormously. Some types of ghost only appear at night. Visibility is low for the player at night.

Weather

The world is filled with many strange weather patterns. (Vivid Weathers) These may also be hallucinations as anti-psychotic meds make the weather less exotic.

Bouts of insanity

Occasionally the protagonist will be plunged into a temporary state of world madness where everything is very strange, disturbing, and dangerous.

The protagonist goes around trying to survive and put the worst of the ghosts to rest. 

The protagonist must also defend themselves against attacking ghosts, which is possible by shooting them. Perhaps shooting ghosts with silver bullets temporarily disrupts them? Or perhaps important symbols have been carved onto the bullets? 

Ghosts

The ghosts are terrifying. They haunt the world. They attack the living.

The way the ghosts are ultimately put to rest is by telling the story of the ghost in text. Having the ghost’s story nearby either appeases and calms the ghost, or perhaps traps them. Either way, it is important that the text be durable and accurate. Accurate because false stories are worse than useless. Durable because a story written on cardboard will rot soon and then the ghost will return to haunting. 

Symbols

The ghosts are vulnerable to symbols which were important to them when they were alive. Thus christian ghosts are vulnerable to crosses. Ghosts who respected the authority of the police are vulnerable to badges. Ghosts who respected wealth are vulnerable to silver, and especially to gold. 

Vulnerable means that the ghosts can’t penetrate symbols which are adhered to armor. They also are temporarily disrupted by weapons bearing those symbols. 

necessary mods(?):

Start me up variant

Vivid Weathers

Pistol

Knife

Sword

Assault rifle

Armor set

Grim variant for nightmare mode

Raider, supermutant, ghoul replacers (ghosts)

Random ghost spawner

Unique human companions

Tattoo mod which produces game effects

Map replacement?

Silent protagonist

Human NPC deleter

Horizon?

Custom survival?

Innocents

Use settlement building mechanics to allow player to create mass headstones in order to pacify ghost hotspots?

Spooky music

Mounds of bones

Nuclear powered (tritium gas mixed with phosphors or fluorescent gasses) neon signs still glow with menacing messages including:
° It’s all in your head
° no regrets
° It was all a dream
° What have you done?
° You have been warned.

If the ghost dogs haven’t been put to rest, eerie ghost wolf howls will pierce the night.

Weather - Probably utilizes the Vivid Weathers mod
° Fire storm ghosts change the weather to raining firebrands and howling winds.
° radioactive black rain

Huge numbers of vultures perched everywhere. Perhaps located near areas with significant food concentrations? Perhaps they just follow the player, spawning in ever greater numbers the lower the player’s hit points?