Zenitsu hair is about to symbolize the Thunder Breathing he is famous for in the anime, thanks to his electric theme tricks. What caused Zenitsu’s hair to turn yellow, though?
Because of the lightning, Zenitsu’s hair turned yellow. Zenitsu hid under a tree during training with Jigoro Kuwajima, Thunder Hashira, when lightning struck the tree, turning his hair from black to yellow.
Although it was not his natural hue, he kept the hair color for a long time in the series.
Plot Reason For Zenitsu’s Hair Turning Yellow
We have had some time behind the training of Zenitsu and his grandfather, former Thunder Hashira Jigoro Kuwajima, in Chapter # 33. Zenitsu was frustrated because he could not live up to his grandfather’s expectations. He could not complete his demonic training and could only use one breath. This happened before the final test of Zenitsu’s election.
“When I was being financially supported by the woman who eloped with me and was riddled with debt, you saved me! Or, I might have just wanted to be brought up as a swordsman.”
Zenitsu speaking to the Thunder Hashira | Chapter #33
Zenitsu said he wished to fulfill his grandfather’s expectations but could not do so. He expressed great sadness at his performance and feared that the former Hashira hid Zenitsu from shame.
Zenitsu’s grandfather tries to calm him down by telling him he is strong, but lightning strikes at the tree where he is hanging.
“What an unpleasant life… I got struck by lightning and my hair color changed. I was thankful for just being alive.”
Zenitsu’s inner thoughts after the lightning strike | Chapter #33
Zenitsu’s hair has been yellow ever since. Thunder Hashira taught him that Zenitsu being struck by lightning might be considered a communication from higher powers.
So you have it. Because he was struck by lightning while training with Thunder Hashira, Zenitsu’s hair turned yellow, and her natural hair color was black. It would make sense that lightning strikes symbolize some awakening of Zenitsu’s respiratory system because of his breathing habits and the king’s ability.