Another reason why Sumi join the resistance was because the founding member of the team Irene's mother Ki knew his father. She told him if he's ready she would tell him all about his father. Since Sumi was curious to know who he was Ki tells him that he was a kind man and a brave warrior who fought for the right reasons. She even tells him how must the two are a like the way they wanted to join the team and their courage are so similar.
