is demon slayer: kimetsu no yaiba episode 18 filler?

Tanjiro and Inosuke face off against the father of the Spider Demons of Mount Natagumo. Tanjiro unleashes an attack, only to get hurled away by the demon’s overwhelming power.

Landing near a river, he comes upon a young demon Rui torturing his demon sister. Hearing Rui call their bonds of terror and hatred “family ties,” Tanjiro is enraged.

So begins the battle between Rui and Tanjiro.