The ultimate villain of Demon Slayer: Kimetsu no Yaiba, Muzan Kibutsuji, didn't become personally involved in the battle wit the Demon Slayer Corps until the manga's final arc. Before that, the six Upper-Ranks of the Twelve Kizuki served as the primary antagonists for much of the story. The defeat of Enmu, Lower-Rank One, during the "Mugen Train" arc marked the last time Tanjiro Kamado would fight anyone other than the strongest demons.
Source：https://www.cbr.com/demon-slayer-manga-spoilers-every-upper-rank-final-fate/
