Yes and no. You could say it's a BL because it has some queer aspects, but it's not tagged as such because the main story isn't about being a romance. It's a coming-of-age horror story and the main focus isn't about two boys in love. That's why the BL tag isn't on here. Mokumouren never put a BL tag on this story.
just check out what the author says himself, either on X or blysky https://bsky.app/profile/mokmok-len.bsky.social
google translate will help you
Mokumokuren* fucc
Well it isn’t a boys love romance story, Bl is usually used for romance. It is a coming of age story with queer characters and horror themes. The queer aspect is heavy but it isnt directly romance
Is this really BL? The anime doesn't have a BL tag on it so I was just wondering if some of you can inform me if the author decided to remove the bl tag ? （￣へ￣）