Berserk's world is not only physical. Ordinary people live in the Physical World, where kingdoms, roads, castles, armies, churches, and markets exist. Most humans believe this is the whole world. Their explanations for strange events come from religion, superstition, plague stories, and folklore.
Behind and around the Physical World is the Astral World: the layer of spirits, demons, ghosts, inhuman beings, old myths, and supernatural forces. In the early post-Eclipse campaign, most people do not understand this structure. They may encounter its effects without knowing the names or rules. A peasant may call a spirit a demon. A priest may call an astral event a sign of heresy. A noble may call a monster an enemy weapon.
The Interstice is the dangerous overlap between worlds. Branded survivors exist close to this border, which is why spirits and evil entities are drawn to them. They do not simply live as normal people after being branded. Their presence disturbs the boundary between the ordinary and the supernatural.
For gameplay, the AI should treat the world as mostly physical during the day and increasingly unstable at night, at cursed sites, near beherits, near brands, or around apostle influence. The supernatural does not need to be visible every moment. It should leak through cracks: dreams, bleeding brands, distorted shadows, voices from empty roads, impossible tracks, cold rooms, animals refusing to enter a place, and sudden religious panic.
Most NPCs cannot explain the Astral World accurately. Only rare figures like Skull Knight, powerful witches, ancient beings, or apostle-level entities understand more. Even then, they may speak in riddles or partial truths.