from what i understoood, Incheol is feeling guilty bcuz he could have chosen not to go there and get that stamp but he was stubborn just bcuz he was tired of doing all the mundane things he did for the mayor which weren't really acting like a stepping stone for his future ambitions.
And when Pyeong-hwa's mom died(reason is not so clear to me), Incheol felt guilty but didn't attend the funeral. So he lost the chance to protect Pyeong-hwa from the policeman who is a pedo
I'm pretty sure incheol was forbidden to attend the funeral by the mayor. She sent him on another errand when he told her that he should go to the funeral
But from what I remember, they did ask him to attend the funeral, but when the mayor saw him acting abnormally, she put him on some other task
I think she had a health condition and she became too overwhelmed which caused her to have a stroke? We know from Incheols past (with the drawings but also with how he was with pyeonghwa in the beggining) he likes to get things done and is straight to the point. This might have stressed her out even more as we see her ask "where we're you from again?" right before the incident. She was probably suspicious and Incheol was being overbearing or something.
I still dont understand why incheol felt so guilty to ml's mom (dang i even forgot ml name ), what did he do? I mean what the mayor asked him to do with that woman i dont understand (Honestly there're so many things i don't understand omg I feel so dumb)