AU version of the Neineikura headmates, if instead of magical girls, they were all heartsword wielders!
The “what kind of soul gives you what heartsword shape” rules for humans are really well-defined, but less so for Tamaputians. We just know they always draw lei o mano — daggers with blades made of shark teeth.
Although they share a body, Kallie, Atarangi, and Kiki are all individuals, which means they each get their own heartsword.
(Readers, place your bets: If one headmate drew her heartsword, and then switched, would it shapeshift? Or would the next headmate be able to also draw her heartsword, and then dual-wield?)