Myth and History of Sekiro

The Infested/Centipedes - Mukade in both Shinto and Buddhism represent impurity, stagnation, and corruption. Given the undying nature of these individuals, it's fair to assess the centipedes coming from their bodies are physical embodiments of said corruption and stagnation. Their souls are unable to reincarnate (See: Hanbei the Infested, The Senpou Temple embalmed monks, Guardian Ape, Yao ) and reach Nirvana.

Yao and Minamoto Palace - Priestess Yao is based on the legend of a young girl who ate a ningyo and lived for 800 years. Wandered Japan as a Nun ( Or Priestess in this case ). It's implied that the Yao you fight in Sekiro is, in fact, a version of the Yao Bikuni myth. Especially given that the residents of Minamoto Palace are fish creatures with human-like attributes ( Ningyo ). Minamoto itself is a surname bestowed by the Emperor of Japan to a branch family. This, of course, plays into the fact that the Imperial family of Japan is allegedly descended from Otohime herself, a dragon. The Okami women are implied to be based on Japanese history and folklore about female martial artists given they wield naginata.

The Sakura Dragon - Implied to be Kuraokami, the Japanese Dragon God of Rain and Snow. Wields the Chilijido, meant to represent the ties to the country of Japan and "The West", or, in this case, Korea. Sakura blossoms ironically represent the beauty and fragility of life, but the Dragon's Heritage blesses one with longevity and potentially immortality.

The Buddhist Candies of Mt. Senpou - Candies which imbue one with various abilities when eating and assuming a proper mudra, a Buddhist hand or body formation. The Monks of Mt. Senpou are based on Mahayana Buddhism due to their manner of dress and the various inferences to Bodhisattva littered throughout Ashina.

Salt - Used in Shinto rituals to this day in order for purification.

Mibu Village - The Unclean Source, a metaphor for Yomi, or the Japanese land of the dead. None of the people here are able to die or move onward. Basically Shinto Hell.

The Shirahebi - Based on the Fertility and Bountiful Kami Benzaiten.

The Sculptor and the Demon of Hatred - Implied to be the build-up of bad karma and the infestation of an Onryo, or hateful spirit. Kingfisher was killed by the Guardian Ape, and, despite carving the Buddha, the Sculptor eventually succumbs to the Urami ( Resentment ) and transforms into an Aragami ( The Demon of Hatred ).

Shichimen Warriors - Literally the vengeful spirits of the executed vassals of Ashina.

The flowers Jack - The Lotus flower represents Enlightenment in Buddhism. The Guardian Ape and the Flower both survive because while the waters of Minamoto Palace are becoming corrupt the farther they fall from the Divine Realm, droplets of it hit the flower. The Chrysanthemum on the Divine Child of Senpou's sash represents longevity and rejuvenation. Fitting since she's literally immortal.