4 ideas
Silk magnate Sahei Inugami dies leaving his fortune and the family's three heirlooms, an axe, a koto and a chrysanthemum, to Tamayo Nonomiya, an outsider, on condition that she marry one of his three grandsons, Sukekiyo, Suketake or Sukemo. Kindaichi finds that the masked man is an impostor and that the killings grew out of the grandsons' mothers' rivalry over the inheritance.
A murder that looks elaborately designed may be the combined result of several people acting separately: a killer, someone concealing the crime to protect a relative, and people pursuing unrelated schemes. Each person's intervention adds details that seem meaningful but belong to different motives. The detective must separate these layers instead of assuming one mastermind planned the whole pattern.
When a person's face cannot be seen, the whole social system of recognition fails, and identity can only be checked through indirect proofs such as handprints, memories and testimony. The masked returning soldier reflects postwar conditions in which men came home changed or unrecognizable. Any claim to be a particular person becomes open to doubt and can be exploited by an impostor.
A will that makes inheritance depend on winning one designated person turns family members into competitors for a single prize. This gives each branch of the family a motive to eliminate the others. Old grievances, here the patriarch's mistreatment of his mistresses and their children, get channeled through the legal document, so the dead man's resentments keep acting on the living.