Yu Ra and Taegu were the youngest kids that arrived in the training camp.
Manager Oh was the fiercesome girl teenager Yu Ra and Taegu watched when they arrived.
At that time, the Union was the Korean government's secret organization. Or, to be exact, Black OPS. Meaning, it's not in the books, it is unsanctioned. The politicians and the public must never know it exists. And if the agents are caught, the government will deny any involvement, they are on their own.
Later, more likely after the Martial Law government collapsed, the Old Union was also dissolved. After all, with no support from the government; and with the new government unaware of its existence, there is no point continuing the Union.
Much later, Taegu decided to reform the organization. The New Union under Taegu's control, is a crime syndicate. Far from the original purpose of the Old Union.
Taegu needs to kill all the original members of the Old Union because for him:
They destroyed their lives.
For the New Union to work in secret, the Old Union must all be killed. They are liabilities. They may share the secret story of the Union, just like what Butterfly is doing.
For him, they are traitors. If they don't join him, then they must die.
