A specific character design feature of Arknights. In the backstory, characters infected with "oripathy" from exposure to the mineral originium eventually have originium begin to fuse with their cells; this creates "oripathy lesions" both internally and externally. These appear as originium "chips" on the body and are present in a number of the character designs for characters in the game. It is not present on all characters, however, since not every operator or character is necessarily infected (or does not yet have external lesions).
It is also a feature that many fan artists, particularly ones who are not very familiar with the property, often miss. Characters that should have oripathy lesions are often missing them in fan art and even the official art can be a little inconsistent about it (Ifrit's Elite II art is an infamous example).