is demon slayer: kimetsu no yaiba episode 52 filler?

With Kotetsu's help Muichiro finally manages to escape from Gyokko's Blood Demon Art, but he is close to reaching his limit with all of the damage he has sustained. As the goldfish demons draw closer to the battered Muichiro and Kotetsu, Muichiro's memories is awakened the very moment the demons attack.

In this memory, he remembers his father, a lumberman, his mother, and his older twin brother, Yuichiro...