There are six forms, but Zenitsu could only learn the first form said to be the basis for the others yet he honed it to where he could fight against several strong demons. He later created a seventh form and defeated his former senior who had become the Upper Rank Six of the Twelve Kizuki.

Will Zenitsu learn other form?

Zenitsu has learned and mastered only the first form of Thunder Breathing, although he knows a total of three variations of this form. This was the basic form he had to learn, but he never mastered the others, although he could because he knows that basic form.

Does Zenitsu learn all Thunder forms?

The First Form: Thunderclap and Flash is stated to be the basis for all the other forms; this was all Zenitsu could learn and hone, while Kaigaku couldn't learn it despite learning the other forms after it.