Zenitsu’s “Godlike Speed” offers an insane amount of acceleration for a decent period of time. But how did Inosuke catch up to Zenitsu?
Inosuke is able to catch up to Zenitsu when the “Godlike Speed” slows down. Zenitsu’s form loses power the longer it goes on, allowing Inosuke to catch up and help him defeat Daki.
While Inosuke and Zenitsu attack Daki, Tanjiro is able to slice off Gyutaro’s head at the same time.
Inosuke is able to catch up to Zenitsu’s speed
In chapter 94, the fight against Gyutaro and Daki is slowly coming to a climax. Despite being poisoned several times, Tanjiro and the other Demon Slayers are able to successfully keep up with the brutal strength and speed of Upper Rank 6.
Gyutaro takes his poison scythe and hits Tanjiro through the jaw, breaking it. Despite the intense pain, Tanjiro knows this is his last chance to be within striking distance of the demon.
He musters the strength all throughout his body, unintentionally revealing a Demon Slayer mark on his forehead. Originally, the audience is informed that the scar on Tanjiro’s forehead comes from a falling brazier at his family home. The tiny scar is then covered by a large Demon Slayer mark.
Amazingly, Tanjiro’s sword begins to cut through Gyutaro’s neck. The demon does not panic, however, as both his and his sister’s neck must be cut simultaneously to be defeated.
We then see Daki, who is now mocking Zenitsu. The Lightning Slayer is able to use his First Form “Godlike Speed” variation in order to overwhelm and immobilize Daki. As the technique goes on, the speed reduces itself.
Due to this reduced speed, Inosuke is able to catch up to Zenitsu. Daki is incapable of defending herself against Zenitsu and Inosuke at the same time, so she calls out to her brother for help.
The combined strength of Tanjiro, Zenitsu, and Inosuke creates the ability to slash Gyutaro and Daki’s necks at the same time.
So that’s the answer. Inosuke is able to catch up to Zenitsu as the “Godlike Speed” form begins to slow down. Zenitsu’s form begins to run out of steam, allowing Inosuke to catch up and help defeat Daki.