These are perhaps the best Demon Slayer episodes focused on Zenitsu Agatsuma.

Zenitsu does not awaken the demon slayer mark, defeating Kaigaku with a new technique instead. To unlock the mark, one must survive life-threatening conditions and have contact with a marked demon ...

The contents of Zenitsu’s letter make a significant difference during the Infinity Castle arc and here’s why.

Demon Slayer's Zenitsu will have a chance to shine in the Infinity Castle Arc as he will fight the most difficult battle of his life.

As the Demon Slayer Infinity Castle movie revealed, the letter carried news regarding both Zenitsu and Kaigaku's former master and the former Thunder Hashira, Jigoro Kuwajima.