nanami has had many close death encounters. he is a jujutsu sorcerer, he looks death in the eyes every mission no matter how little. he had never truly felt so close to death until mahito, until he he was trapped and could have died with a single touch. at that moment, he truly had no regrets. he had fought and fought and like many, would succumb to death. he should have known then, that he was not going to die. jujutsu sorcerers die with regret. they die wishing they had the chance to do one last thing. change one aspect of their life. so when nanami did truly die, he felt those regrets. he wished he could have said something better to yuuji, he wished his last words were not a burden. he wished he could have said goodbye to gojo, shook hands with his students one last time. he wished he could have lived just a bit more, take a stroll through a park. see what the cafe girl was up to, tell her thank you. accept her thanks in return. but he was a jujutsu sorcerer. and jujutsu sorcerers died with regret, and so he did as well.