Sukuna's tattoos differentiate him from Yuji when he takes control. His tattoos reflect the marking of criminals in Japan's history. The markings symbolize Sukuna's cursed energy and techniques ...

We have been shown Sukuna’s true form in flashbacks before now, but Jujutsu Kaisen has revived it at last. Megumi’s possessed form is gone, and of course, Sukuna gave up Yuji’s body recently.