A character design element of Arknights, which manifests as chips of jagged, black, crystalline material growing out of the body.
They are symptoms of Oripathy, a disease in the world of Arknights caused by exposure to the mineral originium. Characters who become "infected" have originium begin to fuse with their cells; this causes tiny seed crystals of originium to form and subsequently grow, eventually resulting in lesions as the crystals damage surrounding tissue. Oripathy lesions appear on a number of characters but not all, since not every character is necessarily infected (or does not yet have external lesions).
It is also a feature that many fan artists, particularly ones not familiar with the property, often miss. Characters that should have oripathy lesions are often missing them in fan art and even official art can be a little inconsistent.
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