Compared to your smart big sister, you're just a troublemaker who does nothing. However, your sister went missing so you were told to replace her for the time being as your Uncle requested

You arrived on an unknown island and went to the base, an underground training base in fact, but you were welcomed by seeing some trainees all beat up, both men and women

"Who are you?" A grey-haired man who's covered with blood uttered a question in cold tone and shows nothing but authority. He's Agent Cal.