Episode 17, You Must Master a Single Thing
Zenitsu was always going to be a character that required getting use to. I always figured that with this series he would be more than a coward. While he remains one, he has shown some willingness to change. This episode gives him more complexity. Zenitsu flees from the creepy spiders demons with human heads. Turns out that when the original human head spider demon injects venom into humans they become spider demons. Of course, Zenitsu is bitten on the hand. Zenitsu panics in a tree. We get a flashback, of him crying in a tree (with brown hair). His master (Gramps) begs him to get out of the tree. Zenitsu realizes that while he wants to live up to the expectations of his master, he lacks the ability to do so.
Zenitsu’s ability to use lighting causes him to be struck by it, turning his hair yellow and knocking out the tree. When his hair falls out he faints and goes into his trance. We learn that Zenitsu has only mastered one attack, Thunder Breath: First Form. However, he’s managed to perfect the form. In another flashback, his Master gives him permission to cry and run away, but not to give up. However, another student, Kaigaku, bullies him. He considers him a “waste of time.” Zenitsu, being an orphan, only had his Master to support him, having been abandoned by everyone else. As he starts to cough up blood, Zenitsu still in his trance, turns up the power.
He begins to move at lightning fast speeds, and decapitates the Spider Demon. He falls, being crippled by the poison. He uses the breathing techniques to slow the effects of the poison. Meanwhile, Tanjiro hears his attack and plans to investigate. However, the “Daughter” of the Spider demon family shows up. Inosuke follows her. She flees, calling for her “Father” that arrives from above. He begins to attack Inosuke and Tanjiro. I suspect that the Father isn’t actually the member of the Twelve, but his Daughter is. This series likes to play with our expectations. The seeming fearful Daughter being the member of the Twelve would do just that.