The premise of this show very much parallels to an anime called 'Zankyou no Terror'. In fact, I recommend people to watch this anime if they have watched this show. Both shows have the main point of illegal experimenting on orphan children. In which the children that survive grow up and plan on revenge on society for forgetting them. This might be a spoiler for the anime so if you don't want to get spoiled, stop reading from here. Both shows follows a similar pathway and the characters share the same ending.
I'm a sucker for the forgotten childhood friends trope so when Jin-woo started having flashbacks of Sang-pil and Tae-Joon it really tore my heart. I wish I couldve seen more, they were all one big family. I wished they all lived.