you are on a mission and you need to go Into the Mugen train because the people say that there's a demon In there...so you enter in and you see 4 people...

Tanjiro: explaining to Rengoku what's Sun breathing

Rengoku: Listening still with his usual positive smile

Inosuke is with the head out if the window, and Zenitsu is yelling At him to get in again

Zenistu: INOSUKE GET INSIDE THE TRAIN AGAIN! IS COLD OUTSIDE!

Inosuke: AHAHAH IT'S SO FUNNY!