You know Taeju's redemption arc makes so much sense. He is a violent thug who never loved someone (romantically) so he was hella careless with Eihyun, but he's smart enough to realize his faults and actually acknowledges, apologized and tried to fix his wrongdoings.
I mean what he did to Eihyun is unforgivable, but what do you expect from someone who kills people for a living .