bare bone, bad, wrong, death radical (n. 78)
歹 centers on the idea of death and decay: a bare bone, something bad or wrong, and the radical used in characters related to death.
歹 is a pictograph of a bare bone or skeletal remains, representing death or decay. Its exact ancient form is uncertain, but the association with death is well established.
The shape 歹 looks like a stripped-down bone or a broken skeleton, evoking death and bad things.
For ガツ, imagine a ghastly bare bone that makes you gasp: ghastly -> ガツ, and the bone is a sign of death.
—
kanji "bare bone" radical at left