People usually associate metal with fantasy and some try to create some metal inspired rpg or stuff but usually fall into cliches.
Lets try to do it right.
Lets try with doom metal.
Doom metal characteristics are:
-Slow to super slow speed.
-Long to super long song lenghts.
-Impending doom themes.
-Depressive themes
-Obscure themes
-Hoplessness themes
-Slow pacing
-Hard to very hard songs
-Minimalism