Despite not knowing much about Gu Reum, Zi 0 decides to trust her and follow her quest for the truth, which takes them to a mysterious church. Not only is the church related to the hidden truth Gu Reum is trying to uncover about her parents, but it's also where Zi 0 stayed there during his childhood. But rather than give answers, the visit brings out more questions about Zi 0's past, his biology, and humanity as a whole. But more so, it causes him to lose control, evoking fear and turmoil in him and those around him.
Watching this episode, I finally get what this drama is about; the consequences of when man's immortality goes beyond just the material in this world. Everybody keeps telling Zi 0 he isn't human, but I only see a man protecting the only person he's felt safe around by staying away from her. But worse than all that was the revelation, Gu Reum's parents were somehow involved in the making of Zi 0, and their disappearance may be related to that rather than to Zi 0 himself. I can only imagine how devastated Gu Reum will get when she finds out the ugly truth.
It's so true when they say we do not fear the unknown. We fear what we think we know about the unknown. Only now does the opening scene from the first episode make sense, that person who threw Zi 0, telling him to remember, he wasn't a monster. Zi 0 getting some of his memories in the church was painful to watch. I hope he remembers what that person told him. Monsters are made, not born; the real monsters are those who made Lee Son, Yoo Na, and anyone else into what they've become. And despite trying to regain his memories, Zi 0 finds himself in a dogged chase for his life by unknown pursuers, including Gu Reum, who believes him to be the only person who may know the whereabouts of her family.