this is just an opinion but,

galraei's horny ass June 29, 2018 12:23 pm

I think the reason Koogi changed the appearance of Sangwoo's father from an old, overweight type of guy (as seen in chapter 5) to a young handsome business man was to further portray the idea that even seemingly normal people can be psychotic and abusive. This might not be the reason for the design change but it's just what I thought of while crying *painful smiling*

Responses
    galraei's horny ass June 30, 2018 12:49 am
    This reply will be showed after approved! yaoi-luv

    yeah I think that might be part of it too, especially how Sangwoo stresses about how his behavior is 'becoming like his father'