Gantetsu

is a former Shinobazu, or criminal ninja.

Background
While he was a member of the group he began to feel guilty for what he was doing, and saved the children from the houses they razed, hiding them in the Forest of Bewilderment with some of the money that he had stolen. Despite this, he knows that he can never completely atone for his crimes.

Shinobazu arc
Gantetsu was captured and was to be taken to a local capital city. On the trip down a river, his comrades, Shura and Monju, attacked a prison ship; while it was initially thought that they had been planning to rescue him, they were looking for him in order to find the money that he had hidden away. Although Todoroki did not trust him, and tried to kill him on more than one occasion, Gantetsu repeatedly helped the group navigate the forest and defeat the Shinobazu members, even saving Todoroki's life. Todoroki agreed to falsely report that he had died in order to allow him to remain with his orphans.