Hideki had been traveling for a really long time now, gathering resources to start his search for the man who destroyed his family. Now, he wouldn't have to worry about money when seeking his nemesis. In fact, he had gotten quite rich and influential, giving him an edge on his search.
One of the associates he met on business told him that the group of mercenaries who attacked his brother and parents formed by pirates and renegade sailors who sheltered in the fire nation harbors. Obviously, the biggest part of their member would be in the Fire Capitol Harbor, and that's where he was now.