Materia runs entirely in your browser — nothing to download, nothing to install. You bring exactly one thing: a key from an AI provider. Here's the whole setup, start to finish. It takes about two minutes.
A browser · An xAI (Grok) key · ~2 minutes · Free worlds
Get your free Grok API key
Head to x.ai/api, create an account, and generate an API key from your dashboard — it takes a few minutes. Grok (xAI) is what every engine is tuned for. ChatGPT and Gemini keys also work if you already have one, but the experience won't be the same.
Get a key at x.ai/api →Open a free world & paste your key
Jump into a free World Engine and open the Settings screen, then paste your key in. It's stored locally on your own device — never sent to us, never shared. There are only ever two connections: you, and your AI.
Build your character & play
Create your character and step in. From there the world is yours — it tracks your choices, your relationships, and your condition, and remembers all of it. Make a mistake and you pay for it. If something dies, it stays dead.
Pick a world →What does it actually cost?
The worlds are free. Your only cost is your own AI usage, billed by xAI — typically a matter of cents per session, not dollars. Materia compresses long sessions to keep it minimal, and MarrowMyth takes none of it; every cent goes straight to your provider. Most players spend less in a month than on a single cup of coffee.
Ready?
Step Into a World.
Three worlds are live and free right now — Resident Evil: Rebirth, Fallout: The Windy Wasteland, and FFVII: Reclaimed. Grab a key, pick one, and go.