How To Get Pure Black World Tendency

Some games use an alignment system or reputation to measure the impact of your actions, but Demon's Souls does things differently. Your character has its own tendency, as does the world, and they can be different, which can make things a bit complicated. At the start of the game, both are neutral, but killing certain characters will shift your tendency towards Black or White, as will your own deaths. It's a gradual mechanic, with several different stages in between Pure Black and Pure White.

Before we get started, it should be said that your tendency has no impact on the game's endings.

By going into the menus, you can check the Tendency tab to find out your character's morality, but reading a world's Tendency is a bit more complex. Inside the world tab, you'll see a collection of archstones. If the archstone is white and illuminated, then your actions have resulted in a White Tendency, but if the statue is dark and unlit, then that world has a Dark Tendency.

How Does Tendency Affect the World?

Overall, Tendency affects the world in 3 ways:

The game becomes harder if you trend towards Black Tendency, both for Character and World Tendency. You'll suffer penalties to your maximum HP and enemies will deal more damage. Trending towards White Tendency, on the other hand, makes the game easier for the player.
You'll have greater rewards in Black Tendency, with enemies dropping more souls and better items, while being in White Tendency will have the opposite effect. This is particularly noticeable when it comes to grinding for Sharpening Stones and how the game treats Crystal Lizard spawns.
Certain objects, characters, and quests are only available in certain conditions. For example, you'll need a pure White or Black tendency to find a specific object at certain locations. This makes it so that doing and seeing everything on a single playthrough is impossible.
Sometimes, your tendency may also unlock a door or a path. This mechanic incentivises revisiting zones once you've obtained a pure tendency of either orientation.

How to Change Your World Tendency

Changing a World's Tendency can be rather difficult, as each of the 5 regions in Demon's Souls has its own tendency linked to its unique archstone. They all operate independently of one another, so it's entirely possible to have a region in Pure White and another in Pure Black at the same time. It's a fascinating system that allows you to pick and choose which items or quests you wish to unlock.
Killing a boss will push the World Tendency towards White, making it impossible to avoid some degree of white on your playthrough.
Dying in human form within a region will push its World Tendency towards black, making repeatedly killing yourself in human form the quickest way to send a world's tendency into the Black
When a world's tendency begins to change, special NPCs will appear, which either allows you to further send the world's tendency in that direction, or to rectify the changes.
Once you've built up a good amount of black tendency, a Primeval Demon will appear, and defeating it will give you a good amount of progression towards White Tendency. It will also drop a colourless demon soul that can be exchanged for the Recovery spell.

Numerous NPCs will offer you quests and rewards if your World Tendency is White. On the other hand, killing them will quickly send your Character Tendency into the Black.
Once your Tendency is black enough, constantly aggressive Black Phantoms engulfed in a red aura will appear in your region. Killing them will allow you to get your hands on unique items and will also send your World and Character tendency towards the White.