Nobody really now what happened to Harlock when he was a kid, except for Natsu. What happened was that they were separated when they first entered the guild and as they went in a job. Harlock was just in plain fear, he had never felt that fear before. One night, when Harlock was captured they injected him with needles, everywhere, he was feeling sacred and sad. He wad powerless in that time.
The next years were just a blur, like it all in a dream, I mean, a nightmare. He wasn't himself, he felt useless, scared, terrified and last one of all sad. He was the opposite of himself, he was another man. "This is my fear" Harlock said murmuring to himself and a shamed. Now he is bound to find the people who did this and swared to find justice.