Ban has been many times chopped, he even has been cut in half, but none of those injuries had left a scar. But Meliodas attack on him has left him a permanent scar. Why is this so? Why Ban's scar made by Meliodas didnt completely heal?
This is due to the technique Meliodas used to inflict the wound: HellBlaze
This abillity nullifies regenerative powers, but also the power of immortality.
Meaning this power could actually kill even the immortal Ban.
As this power also stopped his regenerative power on that spot, the wound never managed to fully heal back in accordance with his immortal regenerative power.
But instead regenerates as a normal wound would have, by scaring.
Hellblaze is a dark and mysterious power connected to the Demon Clan. It allows the user to generate and control black flames that cannot be extinguished. In addition to its immensely devastating power, the flames also nullify any regenerative abilities including that of an immortal.