SCARS
606 got alot of scars during his battle with A-707 + some he gave himself.
He used his arms for a shield, got his torso and shoulders carved by 707's sword, got his mask ripped off forcefully, tried to hang himself but failed, and so he just ends up slashing his own arms
606 never likes to show his scars, hell, won't even look at them, and so he always wears a lot of long sleeved shirts (as for short sleeved, he just wears a jacket, coat, and/or sweater), just because he doesn't want to be constantly reminded
Part of my plan to rewrite 606's lore (Musakui will be in the lore, and for this particular post, might confront/comfort 606)