From the Introduction:
Miasma is a game where you play a samurai, infected by a dark miasma that has held the Imperial Capital in its grip for centuries. In this game, you will wage desperate battles against the monsters that appeared in the wake of the miasma. To stop the monsters from overtaking all of the land, you will become a monster yourself, and commit your body and soul to the fight.
The coming of the Miasma
Centuries ago, something went terribly wrong when the Emperor, representative of the divine on Earth, conducted a ritual to ensure a good harvest. Instead of a blessing upon the land, foul and dark miasma emanated. Within moments, the Imperial palace was enveloped by this foul vapor.
Soon, the survivors found themselves attacked by all sorts of monsters: the dark miasma had infected man and animal alike, creating the monstrous Yõkai.
The non-infected were attacked, and those who survived the initial onslaught had to flee the city, leaving everything behind, lucky to escape with their lives.
The miasma expanded more and more, but eventually settled around the capital and the surrounding lands: a blighted, ruined place, where demons and monsters stalk those who dare to trespass. But even outside of that sphere, the influence of the miasma can be found. Occasionally, people become infected with the miasma. A dark, circular mark somewhere on their body betrays their brush with darkness. These people are exiled, and forced to live under the shadow of the capital.
Some of the infected decide to take up arms against the tide of darkness, to protect the home they have been expelled from. There are even some who voluntarily choose to join the fight: it is a stage for bravery and of hard-won victories against the dark.
You play as one of these warriors, who use the miasma's influence to become stronger, to fight back against that which has taken everything from you.
The game is played without dice: not luck, but planning and commitment to those plans, will see you through.