Item from soul-eater by
A corrupted soul that has begun consuming other souls outside legal sanction — the primary target of Shibusen students and the lowest rung of the pre-kishin corruption ladder.
A Kishin Egg is what happens to a human soul when fear, ambition, or simple hunger drives them to start consuming others. The first illegal soul changes something. By the third or fourth the person is no longer primarily a person. The soul distorts around its acquisitions, growing larger and more unstable, and the human's behavior shifts to match. They are both the threat that justifies Shibusen's entire existence and the tragedy built into that justification: these are people who crossed a line, often a comprehensible one. The weapons that collect their souls are building toward Death Scythe status on the bones of individual human failures. The series doesn't let you forget this.
When perceived through soul-sight, a Kishin Egg soul appears distorted — reddish, irregular, with a faint suppurating quality that distinguishes it from healthy human or animal souls. The human carrying it usually looks normal until they don't. The moment of transformation shows the soul trying to become something larger than the body can contain.
Also known as: Kishin Egg, Corrupt Soul, Evil Human Soul