Is Muichiro a guy?

Is Muichiro a guy?

Muichiro is a short, muscular young man of light complexion with long, straight hair of a black color that fades to mint green as it approaches his waist. ... His eyes and hair are traits shared with his twin brother, Yuichiro Tokito. Muichiro wears a dark, slightly turquoise-tinted version of the Demon Slayer uniform.

Why is Muzan so afraid of Tanjiro?

As mentioned, it is revealed that Muzan's desire to destroy Tanjiro stemmed from his hatred towards his previous nemesis, Yoriichi Tsugikuni.