Demon Slayer's third season gave protagonist Tanjiro Kamado plenty of growth, including his training with that six-armed mechanical doll and his incredible performance against ever-stronger Upper Moons, like Hantengu. Tanjiro even performed a high-speed move reminiscent of Zenitsu's thunder breathing, which calls into question whether Tanjiro even needs Zenitsu in his squad anymore.
Zenitsu Agatsuma is stronger than his fearful dandere personality would suggest, and he showed some growth of his own while fighting Daki. That said, the other demon slayers are rapidly learning and using newer and better moves, while Zenitsu's only strategy is to move fast like a lightning bolt — and now Tanjiro can do it, too. Zenitsu needs to up his game if he's going to remain relevant in Demon Slayer in the wake of Season 3's events.
Zenitsu Has Become Obsolete In Tanjiro's Squad
Zenitsu Agatsuma may be the butt of many jokes concerning his obnoxious personality and unflattering cowardice, but his biggest problem is his lack of a unique combat ability. Even if all demon slayers use swords to fight, different breathing styles yield different results, limiting the redundancy between demon slayers. Zenitsu wowed Demon Slayer fans early on with his linear, lightning-fast moves when he falls asleep, but by now, super-speed is nothing special. Zenitsu did well against Daki with his quick moves, but it was Tanjiro and Tengen Uzui who finished the fight, while Zenitsu and Inosuke merely held Daki off to buy time.
Now, Demon Slayer's best heroes have taken further steps to enhance and diversify their moves, and Zenitsu missed out, as did Inosuke. Genya is like a half-other who powers up from eating demon flesh and even uses shotguns, while Tanjiro can use Hinokami Kagura and even borrowed the super-speed of Zenitsu's trademark technique to catch up to a fleeing Hantengu. Inosuke, meanwhile, has a unique, self-taught beast beathing style that can take even veteran demons by surprise, and he can sense all demons in the area with his instincts, too. In light of all this, Zenitsu currently has nothing special to offer to the series' main trio of shonen heroes, and he must change that at once.
Zenitsu Must Get Creative & Look Deep Within Himself
With the Swordsmith Village now safe from the Upper Moons, Tanjiro and his friends have an opportunity to train some more before the next battle, and Zenitsu needs it more than anyone. He no longer has a special move or unique ability in mind, with Tanjiro able to emulate his super-speed, so it's time to get creative. After all, resourceful creativity is the Demon Slayer Corps' best weapon against demon-kind, from Shinobu Kocho's poisons to Tengen's ninja weapons and Genya's shotgun, and Zenitsu must embrace that mentality to keep earning his place in Tanjiro's squad.
Zenitsu's new training could give him clever new techniques with thunder breathing that don't just rely on sheer speed, and completing this training could empower Zenitsu to help him overcome his cowardly streak. Zenitsu could also look deep within himself to figure out exactly why he fights and why he's part of Tanjiro's squad, which could motivate him to undergo and complete that special training. Tanjiro's "why" is already firmly rooted in place, and he will learn anything he must to protect Nezuko and find a cure for her. Similarly, Genya Shinazugawa's "why" is rooted in avenging his mother and overcoming his own weakness, which drives him to embrace his half-other powers and bring shotguns into battle. Now it's Zenitsu's turn, and not a moment too soon.