Genan Shiranui belongs to the enigmatic Shiranui Clan, practitioners of the "way of darkness" who possess demon heritage, manifesting in his green skin and distinctive, monstrous features considered handsome within his clan. He travels Japan, indiscriminately killing to advance along the "way of evil" and become ruler of all demons. During these travels, he encounters and is slain by an unknown female ninja resembling Mai Shiranui.

Revived in *Samurai Shodown II* by Mizuki Rashoujin, leader of the Demon World, Genan accepts a second life in exchange for servitude while secretly plotting to kill Mizuki and seize control of the Demon World himself. However, in his ending, his wife, Azami, persuades him to abandon his ambitions, and he returns home to live peacefully with her and their children: Zakuro, Mukuro, and Hedora.

Genan wields a claw weapon named Azami, extending via a hidden chain to harpoon opponents. His fighting style incorporates supernatural abilities: spewing poisonous gas by consuming a potion, surrounding his body with fiery energy for a rolling charge, and shedding his skin as a decoy for evasion. Despite his menacing capabilities, he exhibits a light-heartedness and prioritizes his family's well-being. He often displays blustering confidence, declaring himself a king while acting as a minion, and parodies characters like Haohmaru.

In *Samurai Shodown: The Motion Picture*, Genan serves under Amakusa Shiro Tokisada. Dispatched to eliminate the reincarnated Holy Warriors, he confronts Galford D. Weller and meets Jubei Yagyu, who informs him of growing resistance against Amakusa. Later, after Charlotte and Haohmaru escape Amakusa's trap, Genan locates them but is swiftly defeated by Haohmaru embracing his destiny as a Holy Warrior.

According to SNK background designer Tomoki Fukui, an underlying development team backstory involved Genan's clan defeating aliens who attempted to invade Earth, with alien bones appearing in a cauldron within his stage design.