The two unnamed older brothers of Kyōshirō.
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They and their mother were constantly abused by their violent father.
Eventually, they were adopted by a traveler who offered their father a boar in order to have them. Apparently, the traveler took good care of them but they left him when they heard their mother was ill.
The three brothers returned to their home, only to find their mother's skeleton. Bitter towards their father, they were sure he killed her and wanted to kill him in order to make him pay for all he had done. They eventually found their father and trapped him.
The two older brothers told Kyōshirō to stay put and live, as they didn't want their youngest sibling to become a murderer of their own father.
Then, the two brothers committed a suicidal attack by pushing themselves and their father off the cliff. They did this because a killing of one's own father was a horrible crime and they didn't want to live after committing it.
Kyōshirō found and buried their bodies.
See more pictures in Kyōshirō's Siblings/Gallery