The Endu Shrine Gate
The gate the burial-site key actually opens, and the one place in the demo that visibly promises more game behind it.
Once the key turns up, the demo’s geography snaps into focus: the shore teaches you, the forest and crypt slow you down, and the shrine gate is where the leash ends. It is a door with a name attached to the sword you are already carrying, which is the cheapest and most effective kind of promise a demo can make.
The gate itself is not a boss room in the free build. What matters for planning is the shape of the teasing: the demo spends its last minutes pointing at content it does not contain, and does it without a cutscene.
The naming is the whole trick. A generic locked door is scenery; a door labelled with the name of the sword in your hands is a promise about that sword. It tells you the weapon has a history on this island, that the history is gated, and that the gate is a place rather than a menu. None of that requires a line of dialogue.
For anyone using this page to decide on a purchase, the honest reading is that the shrine is evidence of structure rather than of content. It proves the island has locked regions with keys that live somewhere else, which is the shape the official feature list describes when it calls the world interconnected. It does not prove those regions are good, and the demo cannot show you that.