Honestly, I find the 'blood transformation' part of Himiko's quirk way more unsettling than the standard shape-shifting you see elsewhere. It's not just borrowing a face; she has to ingest their blood to copy them perfectly. That adds a whole layer of violation and obsession that ties directly into her messed-up worldview. She doesn't just want to be someone else for a mission; she feels a genuine, twisted love for the people whose forms she takes, wanting to become them entirely because she admires them so much. It's a parody of fandom taken to a lethal extreme.
Her motive starts simple—she's just built different, a natural-born predator who finds joy in the act of stabbing and the sight of blood. But later, it gets more complex. The League gave her a 'family' that accepts her for what she is, and Stain's ideology of purging 'false heroes' gave her a cause to channel her bloodlust into. She's not just a random psycho; she's a broken person who found purpose in a broken system, which makes her way more terrifying and, weirdly, a bit tragic.