Kefkiroth:
I always thought that was part of him being inexperienced. When things go south in a relationship, it’s easy to become angsty, emotional, fearful of losing your relationship, etc. I don’t think it was a “transformation”, just a natural result of his immaturity.
Same thing for post-timeskip. He comes off as cold, because who wouldn’t be after having to deal with all the emotions of your first love again, after that harsh breakup? But by the end of ep 14 he softens up in the bike trail scene, and you even see him in the self-driving test working with SDM.
I think the writer didn't do a great job of portraying immaturity versus maliciousness. Or maybe the actor himself didn't do a good job of portraying the emotions of youth, and instead in came out as manipulative. It also probably didn't help NDS was already 27 years old at this time. There was less sympathy all around.
I think maybe making NDS closer to early 20's, having him be more expressive with his emotions and showing him have remorse for his actions would have done wonders for the NDS character.
Him being stuck in the same place for 3 years shows that he lacked character growth in that time. Are we going to keep excusing NDS behavior due to immaturity, when other people his age have grown considerably, just like Yong San? His friend has already apologized to HJP, are we ever going to see NDS do it?