I love when people draw him with longer hair (I personally always imagined it to be short), so I like to headcanon him having had longer hair in the early books and prior to that!
Of all the characters to appear thus far in the anime, I think Nanami has a particular way of appealing to viewers who are about mid-20 and up. To an audience that's spent time in the work field, that's tried to put in effort for a job that's ultimately a fabrication to make the rich richer and, at best, to not benefit the poor at all, and at worst, actively exploits them and holds them down. To those who have deep questions about the moral fabric of the societal systems they find themselves trapped in, and have questioned their own morality as someone who willingly (if grudgingly) participates in that system.
It's not really a surprise to discover he reflexively protects his soul with cursed energy. Learning to protect your soul is how you weather working under corrupt bosses for nebulous gain. If you can't (and sometimes even when you can), the job will slowly eat away at you, shaping you with its teeth to the perfect cog that it can keep turning until it breaks and is cast aside.
Jujutsu Society might not be much better than the corporate world when it comes to the corruption of those on the top, those who would willingly and too often happily feed the very people they're supposed to protect to a machine they know will destroy them. But at least there, Nanami can embrace a part of him that he tries to keep hidden.
Nanami is, at his core, a protector. Not just physically. When he notices that he and Itadori are fighting humans and not curses, he takes it on himself to do the killing so Itadori doesn't have to get blood on his hands. In Shibuya, his main focus with all the younger and less powerful sorcerers seems to be to get them out of there, even if they could be of help. This isn't because he's underestimating them, but because he doesn't want them hurt. Or hurt more than they've already been hurt.
Jujutsu Society may be just as shit as normal work, but at least there, he can protect others, so he goes back to it knowing full well he's probably signing his own death warrant in doing so.
We can't all find jobs that will allow us to retire young in Malaysia. In fact, most of us won't, and even those who might may find it's not actually worth the cost. But I hope we can at least find a job that's our Jujutsu Society, where maybe it's still shit, but it feeds our soul in a way we need to be fed.