That's what chakra is. Characters constantly establish that chakra, in raw form (no fire/water affinity), is not something physical, as shown in Kidomaru's fight with Neji and that raw chakra actually being visible in cases like Susano;O, Kyuubi cloak, or Kaiten are examples of so much chakra being used that it becomes visible. Not to mention spiritual energy is said to be a component of chakra. Every thing in the Narutoverse uses chakra and the fact that it's used via Susano'O only further proves that.Yata isn't made of chakra. its a supernatural spiritual entity.
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