Much time has passed: The Middle Ages, The Industrial Revolution, The Space Age, The Visitation, The Disaster and Great Declension, The Age of Ice and Darkness, and now ... finally ... The Time of the Red Tide. Yes, the world has moved on. Much has been lost to history, yet some things gained. Welcome to Scarlet Horizons.

The setting of Scarlet Horizons is Asian-themed post-apocalyptic fantasy in Earth's very far future. Most of the world has been consumed by something called the Red Tide, an alien horror that takes the form of a crimson mist, able to corrupt and consume both physically and through dreams.

The remaining population of the world fled to the Sunset Isles, an extensive archipelago located roughly where Great Britain existed many tens of thousands of years ago. There, after driving the native Shou (who replace Orcs, Goblins, Bugbears and Hobgoblins) into the wilderness, they settled and formed new kingdoms.

The world saw unthinkable advances during The Visitation, suffered untold losses during the Great Declension. Sages speculate about what heights of exalted knowledge and fabled technology now lie hidden in the sediment of countless past generations. But for every tomb-plunderer and ruins-seeking archaeologist, there's a minion of the Ninefold Celestial Empire who is set on preventing the uncovering of veiled secrets from antiquity. Such things must remain shrouded, lest one faction or another gain advantage.

There are four major kingdoms in the setting – the failing Mandarinate of Xian, once the ruler of the entire archipelago, the Hellsworn Shogunate of the North, the decadent Magocracy of Tien Lung, and finally the hard-working and faithful monotheistic Hohnberg Pact.

The Thousand And One Islands of the archipelago of the Sunset Isles are home to samaurai and sohei, wu-jen and alchemists, reclusive sorcerers and sublime ascetics at remote monasteries, powerful shoguns in palaces, and fey monsters of the mundane, magical, and (human?) types.

What are referred to as dwarves, elves, and halflings are believed by scholars to share a common ancestor - homo sapiens. What advanced genetic manipulation may have been perpetrated on the human genome during the decades of The Visitation? No records exist anymore ... or do they? Even the shou may in truth descend from humanity.

There are 5 core mechanics to Scarlet Heroes, of which two are specifically designed to allow a lone hero to face a party’s worth of adventure.

Checks
When a character is trying some task of personal prowess or skill that might reasonably tax a hero, roll a check. The difficulty ranges from 9 to 17, and is rolled on 2d8 adding the relevant attribute modifier and their highest relevant trait.

Saving throws
Rolled to avoid traps, magical attacks and other attempts to harm the character, saves have a difficulty of 9 + the HD or Threat of the attacker, and are rolled exactly as Checks are, but adding the character’s level to the result too, meaning you roll 2d8 + level + attribute + highest relevant trait.

Attack rolls
A rolled on 1d20 plus the character’s attack bonus, relevant attribute and the enemy’s armor class. A result of 20 or greater is a hit.

Damage rolls
This is the core of what makes Scarlet Heroes work for a single player whilst otherwise leaving the math and numbers of enemies unchanged.
Instead of reading damage dice straight, damage is read as follows.
 

1: 0
2-5: 1
6-9: 2
10+: 4

Each die is read individually, and damage modifiers apply to a single die. Damage is done to enemy Hit Dice but to player Hit Points. For example, a Skeleton, having 1 HD would go down in one solid hit, and would do between 0-2 points of damage with each successful attack on a PC.

With the exception of a Thief’s ambush damage, overflow damage is applied to the next enemy; a character fighting a group of skeletons rolls 4 damage – four of the skeletons go down.

The Fray die that heroes get is read just like a standard damage dice, and can be applied to any qualifying enemy that the character could reach. The fray die is rolled even if the character isn’t declaring an attack that round.

The end result of all this is to allow a single character to face down threats that would normally require a full party, and to enable the use of pre-written modules without having to re-jig all the encounters.

Defying Death

If a hero is about to die or encounters an obstacle they just can’t get around, they may attempt to defy death. This is done by rolling 1d4 for each of their levels and applying the result as damage. If they’re still standing they survive the threat or get around the obstacle. If they drop to zero, they’re reduced to 1hp and have failed.

Each time the character tries to defy death during an adventure the dice step up by one size, to a maximum size of d12.