I'm already on episode 17 (just finished episode 16), so scram if you're sensitive to spoilers.
This might be far fetched, but I'm beginning to suspect Junichiro Yoshimura, the Yakuza boss, and Yi Soo's supposed savior, of having Yi Soo's sister kidnapped. I think he might be manipulating Yi Soo, that is making Yi Soo think that Chairman Jo is behind all the misery befalling his--Yi Soo's family, to make Yi Soo Yoshimura's instrument in bringing down Gaya Hotel.
Of course the more likely scenario is that Chairman Jo is actually the mass murderer Chang Something Bo and is therefore wrecking havoc on Yi Soo and his family to keep his real identity a secret.
At any rate, the writers have me thoroughly guessing at this point, and I just hope the ending is a good one.