设定系推理 / Setting-Based Mystery

设定系推理 is the genre frame foregrounded in 99.很久很久以前，妖怪也推理啊…. The episode defines it as mystery fiction that first creates a world unlike ordinary reality, then builds a puzzle from that world’s declared physical laws, magical rules, social customs, or supernatural beings.

The important boundary is that the strange premise does not remove logic. In [[MukashiMukashiAruTokoroNiShitaiGaArimashita|《很久很久以前，在某个地方有一具尸体》]], ogres, magic mallets, tiny bodies, talking animals, shapeshifting, time-stopping shells, and repeated-death loops are allowed. But once allowed, they become constraints for [[HonkakuMystery|本格推理]]: who could enter, what could change size, what evidence should remain, and which identity claims still fit.

The source contrasts this with social-school expectations. A reader looking for the psychological or social depth of a realist crime novel may miss the point; this mode is closer to [[PuzzleSnackMystery|推理薯片]] and Absurd Rationality, where pleasure comes from watching a clear rule system produce surprising consequences.

Key Claims

• A non-realistic premise can support fair deduction when the rule is explicit and consistently applied.
• Setting-based mystery shifts the realism question from “could this happen in our world?” to “does this follow from this story world’s rules?”
• Familiar source worlds lower the setup burden; folk tales already tell readers what kinds of beings, objects, taboos, and transformations are possible.
• The form can combine with alibi tricks, locked rooms, closed circles, narrative tricks, time devices, and exchange murder.
• The danger is arbitrary rule addition: if the rule appears only to solve the case, the puzzle loses fair-play force.

Connections

• [[MukashiMukashiAruTokoroNiShitaiGaArimashita|《很久很久以前，在某个地方有一具尸体》]] and [[AoyagiAito|青柳碧人]] - source book and author.
• [[FolkTaleMysteryRewriting|民间故事推理改写]] - the episode’s concrete route into setting-based mystery.
• [[HonkakuMystery|本格推理]] - puzzle tradition the source says setting-based mystery can extend.
• [[IssunBoshi|一寸法师]] and [[SaruKaniGassen|猿蟹合战]] - examples where magical or animal-folk rules become deduction constraints.
• [[PuzzleSnackMystery|推理薯片]], [[ClosedCircleMystery|暴风雪山庄]], and Observation Before Inference - adjacent mystery concepts.
• Absurd Rationality and Nonsense Logic - broader rule-governed absurdity neighbors.