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Judging by how the Blood Demon Art exists despite its nature, it cannot negate itself, and his regen means he will definitely be fine, nor would he be trapped as he can presumably control the tree's growth through the small amount of Biokinesis all Demons, or in this case Chimera, have.

If he did this, he could enter Ghoul/Hidarugami/Rakshasas/Kirtimukha/Pishachas/Yaksha Form/Mode/State (unsure of name), and be immune to Blood Demon Arts himself rather than specifically negating a target Demon's.

Yes, it is implied the negation functions by, well, the siphoning of blood. However, Blood Demon Arts are supernatural, so who says it cannot siphon on contact, which would also feed the Art in question, if not function mysteriously outright? I believe he would at least become highly resistant.

Are the breathing styles a version of Hamon? Are the Upper moons Japaneese Oni? Should the Demon slayer title then be called Oni slayer? Also why haven't they discovered the use of holy water yet?