The Mugen Train arc is one of the best in the Demon Slayer series. But why is Tanjiro on the Mugen Train?
Tanjiro is on the Mugen Train because he wants to meet Rengoku. As the Flame Hashira, Rengoku may shine some light on the “Hinokami Kagura” technique that Tanjiro is keen to master.
His father used flame breathing in the past, so Tanjiro hopes to meet another flame breathing user who can educate him on relevant techniques.
Tanjiro has water powers due to the circumstances of his training and mentor. Naturally, he’s more akin to flame breathing.
Tanjiro boards the Mugen Train
Chapter #53 begins with Tanjiro receiving a medical examination from Shinobu. She clears him for exit, but Tanjiro asks a question before he leaves.
“Have you ever heard of the Hinokami Kagura,” Tanjiro asks. Unsure of the technique, Shinobu answers no. Since Tanjiro’s father uses “fire” breathing, Shinobu summarizes, then Tanjiro might think he can learn something from speaking to a Slayer who also uses fire breathing.
Shinobu clarifies that it’s not called “fire” breathing, but rather flame breathing. She suggests it may be a good idea to ask Rengoku, the Flame Hashira, about the Hinokami Kagura technique. This will be the first time that Tanjiro meets Rengoku.
Fast forward to Tanjiro, Zenitsu, and Inosuke leaving the Butterfly Mansion. They arrive at the Infinity (mugen) train.
Zenitsu exclaims that since the group has not received orders for a new mission, they should have stayed at the mansion. Tanjiro, looking to be proactive after finishing the health treatment and wanting more information from Rengoku, wants to board the train.
The following chapter, the group enters the train and it sets off. After noticing Rengoku repeatedly saying the word “delicious”, there’s a minor skip in time where Tanjiro explains his predicament.
Rengoku, in his usual chipper attitude, says he’s never heard of Hinokami Kagura. The Flame Hashira goes on to explain that flame breathing in general has a long history.
In all ages, Rengoku explains, Flame and Water swordsmen have been among the Hashira. Flame, water, wind, stone, and thunder are the basic types of breathing. All other techniques, such as mist for example, are offshoots of those cores.
So that’s the answer. Tanjiro is on the Mugen Train because he wants to learn more information about Hinokami Kagura. Rengoku, the Flame Hashira, rides the Mugen Train and may be able to provide an explanation to Tanjiro.