Hear me out-because “Yoriichi was just an old family friend of the Kamados” explanation never fully sat right with me. When you start lining all the details, it feels way too convenient.
•Tanjiro scares Muzak so badly that it triggers his fear of Yoriichi. This isn’t just “plot convenience”—Muzan recognizes something in him.
• The Kamado family could use sun breathing when literally no one could. Yoriichi had to create all the other styles just so others could keep up, but the Kamados? They had it naturally.
• Tanjiro looks like a mini Yoriichi, and his dad is basically Yoriichi’d copy. That resemblance is almost suspicious.
• Yoriichi’s mother’s Illness = Tanjiro’s father’s Illness. Both had near identical conditions that made them weak or immobile. Genetic echo?
•Blue spider Lilies. We know Yoriichi’s wife’s Grave had them. Guess who still had access generations later? The Kamados. Tanjiro’s mom even fed the kids blue spider lily soup. Coincidence? I don’t think so.
Now consider this: we see Yoriichi two very different flashbacks— young and strong when the Kamados thank him, then decades later when UpperMoon One meets him as an old man. That’s a huge gap. Are we really supposed believe he never loved again, never had children after his Tragedy? That feels unlikely.
👉My theory: Yoriichi did have another child with someone else, and that bloodline eventually married into the Kamados. Which means Tanjiro isn’t just a kind boy chosen by Fate—he’s literally carrying Yoriichi’s Legacy in his blood.
And honestly that makes Muzak’s defeat so much poetic. The bloodline of the man who almost killed him finally finishes the job centuries later.
Also, if this is true, then Tanjiro and Muichiro’s instant friendship is Hilarious. Descendants of Rival brothers just vibing like “yeah we’re besties now”. 💀