Todoroki

was the captain of the guards on the ship that was transporting Gantetsu.

Background
Years before Naruto, Sakura and Lee had accepted the mission, the Shinobazu had attacked his home, resulting in the deaths of his parents. Todoroki had seen Gantetsu with his hand over his brother's mouth before flaming debris had fallen into the room the two were in. Believing his brother to be dead, Todoroki had trained hard to prepare for the opportunity to avenge him.

Shinobazu Arc
Naruto found Todoroki below decks threatening to kill Gantetsu. Shortly afterward, one of the Shinobazu ninja used a metallic wire technique to slice the ship in half, separating Naruto from everyone besides Gantetsu and Todoroki. Todoroki consistently refused to trust Gantetsu, and eventually tried to kill Naruto and Gantetsu to gain his vengeance and to escape blameless. Upon learning of his brother being alive, Todoroki reluctantly agreed to let Gantetsu help them. Todoroki was reunited with his brother, and told Gantetsu that, while he could never forgive him, he would allow him to remain with his orphans.