ム, ブ, な.い
nothingness, none, ain't, nothing, nil, not
JLPT0 G4 S12 F274
The relevant oracle bone form of this character shows a dancing figure with long sleeves that conceal the arms. To an abbreviated form of this character was eventually appended 火 fire → person/object concealed by dense smoke. *Not*, *none* and *un-* are extended meanings (lack presence/existence ← concealed; compare 亡) → *disregard*; *lose*; *be gone*; *be missing*; *run out of*.
[Full Kanji Etymology List]