The series never gives a canon, fully confirmed answer to who the second demon Muzan created was, and fans generally agree that this detail is left unclear on purpose.

What we do know

  • Muzan is the first demon, created by the Blue Spider Lily medicine given by the unnamed doctor in the Heian period.
  • After becoming a demon, he spent centuries experimenting on humans, turning many into demons, most of whom died from being unable to withstand his blood.
  • The story and official guides focus on strong, long‑lived demons (like Kokushibo, Doma, Akaza, etc.), but they are clearly not the first ones he ever made—just the strongest survivors.

Common fan theories

Because the manga and anime never show “demon #2,” most discussion comes from fan speculation and forum debates.

Some popular guesses are:

  1. Tamayo
    • She was turned into a demon by Muzan centuries before the main story and is explicitly “very old,” making her one of the earliest demons we know about.
 * However, nothing states she was literally the second demon ever.
  1. Kokushibo
    • Kokushibo has existed for about 400 years, making him one of the oldest demons, and he’s Upper Moon One.
 * Still, he appears _long_ after Muzan’s transformation, so he cannot logically be the second demon created.
  1. An unknown, off‑screen demon
    • Many fans think Muzan experimented on numerous humans immediately after becoming a demon, with most failing or dying, so the “second demon” was likely some unnamed person who never became important to the plot.

In fan Q&A threads, the most common answer is that we simply don’t know , and that the author never intended the exact “second demon” to matter to the story.

So, who was it?

If you’re asking in a strict, lore-accurate way:

  • There is no official character identified as “the second demon Muzan created.”
  • Any specific name (Tamayo, Kokushibo, etc.) is fan speculation , not canon confirmation.

TL;DR: The manga and anime never reveal who the second demon Muzan created was, and the identity of that demon is unknown and likely intentionally left unspecified.

Information gathered from public forums or data available on the internet and portrayed here.