Fuurinji Saiga made his first appearance in Battle 192. He is between the ages of 38 and 39, with an unspecified fighting type, likely encompassing both Sei and Dou. Known as a practitioner of Satsujin Ken, he bears the Yami Symbol of Shadow and specializes in Fuurinji Style Martial Arts. As the current One Shadow of Yami's One Shadow Nine Fists, he mentors Kajima Satomi and is the father of Fuurinji Miu, as well as a lost hero of Ryozanpaku.
In his youth, Saiga was characterized by kindness and mercy, sparing opponents to avoid bloodshed. He fell in love with Shizuha and sought her hand in marriage. However, in the present, Saiga appears ruthless, possibly corrupted by constant fighting and an insatiable desire for strong opponents. Within Yami, he likely rules through fear, showing no respect to its members. He has a peculiar habit of concealing his face when speaking with other Yami members. It is heavily suggested that he murdered his wife, Shizuha, and abandoned his daughter to pursue his battles, indicating a lack of concern for his family.
Despite this, during his first full appearance, Saiga demonstrated deep care for his daughter's safety, rescuing her from Jenazad’s brainwashing and preventing her death. He also showed compassion, thanking Kenichi for protecting Miu and acknowledging him as trustworthy. Although seemingly a follower of Satsujin Ken, Saiga displayed mercy towards his enemies, defeating them without killing and even providing Menang with medicine for his injuries.
Saiga was raised by his father, Fuurinji Hayato, who rigorously trained him in the principles of Katsujin Ken, which Saiga upheld until adulthood. Akisame mentioned they were best friends. At some point, Saiga defeated James Shiba, damaging his right eye and left leg, supposedly due to Shiba lowering his guard.
Saiga met Shizuha while bird-watching in the mountains but faced difficulties marrying her because the Kuremisago viewed her as a religious symbol, fearing she would fall into the hands of someone too powerful. This led to a split within the Kuremisago, with some supporting Saiga against tradition and others upholding it, resulting in global conflicts. Saiga managed to hold his own in many matches without killing, but as the battles continued, he began embracing Satsujin Ken. His father noticed this shift but chose to ignore it until after Shizuha's death, which is strongly implied to be Saiga's doing.
