Tanjirou being oblivious.

Tanjiro is chilling, then he is turned into a demon(against his will, because nice) All before the Rui fight. Just before the Rui fight actually.

How would this affect everything?

Please pardon any writing error. English is not my first lenguaje.
obiously, demon slayer does not belong to me. All rights to Koyoharu Gotouge.
Just the story line is mine.
And, also, I watch Demon Slayer in Netflix, not the manga, so a few details may not be present.