Kimetsu no Yaiba: Mugen Ressha-hen
Demon Slayer: Kimetsu no Yaiba Mugen Train Arc
鬼滅の刃 無限列車編
Mugen Ressha-hen adapts chapters 54 to 66 of the manga. The first episode is original to the anime.
Kimetsu no Yaiba - Mugen Ressha-hen