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 《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 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 推理薯片 and Absurd Rationality, where pleasure comes from watching a clear rule system produce surprising consequences.

115.京极夏彦今昔续百鬼：不研究妖怪，怎么好好做人？ clarifies the boundary by contrast through 京极夏彦’s 妖怪推理. The source’s “走科派” yokai mystery is not setting-based in the episode-99 sense: it does not make yokai physically real and then solve inside those rules. It keeps the eerie materials serious while returning the explanation to human action, social conflict, folklore as social memory, and interpretive error.

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.
• Demystifying yokai mystery marks an adjacent but different route: the story may begin with supernatural language, but the final logic asks why people used that language.

Connections

• 《很久很久以前，在某个地方有一具尸体》 and 青柳碧人 - source book and author.
• 民间故事推理改写 - the episode’s concrete route into setting-based mystery.
• 本格推理 - puzzle tradition the source says setting-based mystery can extend.
• 一寸法师 and 猿蟹合战 - examples where magical or animal-folk rules become deduction constraints.
• 推理薯片, 暴风雪山庄, and Observation Before Inference - adjacent mystery concepts.
• Absurd Rationality and Nonsense Logic - broader rule-governed absurdity neighbors.
• 妖怪推理, 京极夏彦, and 《暗眼小僧》 - episode 115’s demystifying contrast case.