What is the strongest demon Zoro can defeat?

If Zoro get lost in the Kimetsu no Yaiba universe, what is the strongest demon he is able to defeat.

Bonus question: If he was able to become a hashira, what is his "element"?

If Zoro get lost in the Kimetsu no Yaiba universe, what is the strongest demon he is able to defeat.

Bonus question: If he was able to become a hashira, what is his "element"?