Zenitsu protects Nezuko and several cars using his Thunder Breathing: First Form while still asleep.
Kyojuro Rengoku finally wakes up and quickly takes command, ordering Tanjiro and Inosuke to find the demon's "neck" while he, Zenitsu, and Nezuko protect the passengers in different train cars. Kimetsu no Yaiba: Mugen Ressha-hen Episode 5
Inosuke’s sharp senses lead him and Tanjiro to the engine room, where they discover the demon's massive neck bones beneath the floorboards. Zenitsu protects Nezuko and several cars using his