Genjuro's design is centered on the scar on his back. Developers wanted to make him a character with "adult appeal" who would leave a lasting impression for the female players. In Gamest's 1997 Heroes Collection, he was ranked the staff's eighteenth favorite character and was the number one favorite character (from the development team and fans) at the time of his debut.
He claims to have killed his family and at least a thousand other people. His mother was a prostitute and, due to her profession, he knows nothing about his father. Even so, he made a silent oath to look after his mother until his father came home. When he was fifteen, Genjuro killed a man who stayed in their home - due to his mother's pleas for protection from her client's drunken rage. While he turned to leave his home for good, she attacked Genjuro while cursing his existence and left the scar on his back. He killed her in retaliation.
Orphaned, Nicotine Caffeine spotted him and took him under his tutelage along with Haohmaru in his home. Both students were close friends yet Genjuro's hunger for power worried Nicotine. To test his students, he tempted them to fight over the treasured sword, Fugudoku. They were tested by facing off with a group of other fighters. Genjuro, believing that "worthless" people don't deserve life, killed his opponents during the competition. He leaves Nicotine's place in disgust after this event. He swore to kill Haohmaru and Nicotine, spiteful for their idealistic beliefs on swordplay. He hates Haohmaru especially, because he resembles the man his mother was with when he killed them. He also was attracted to Shiki at one point, as she resembled his mother.
His profession during his travels is a hitokiri or killer-for-hire, often accepting the more "dirty" jobs such as wiping out pirate brigades and bandit hideouts. His former clients include Sankuro Yorozu and Mizuki Rashojin. In Samurai Shodown 64-2, Genjuro gains the upper hand in his last duel with Haohmaru. Before he could deal the final blow, a boy stabs him in vengeance for his unnamed father. It's heavily implied that Genjuro dies from his wound and, as promised, an older Haohmaru toasts to his friend's honor.
Similar to Ukyo, his death is believed to be retconned in the newer sequel. Here, Genjuro is attacked by two assassins; one he kills quickly and the other somehow survived. Before he makes the killing blow, the surviving assassin tells him that this was a test from a man named Golba and offers him to join his master. As he hesitates, the assassin blows himself up, which perks Genjuro's interest and begins his journey to find Golba. He is still alive in his ending and is on another job as usual.
He has a motto that he recites before he goes to slaughter people. It's roughly translated as:
"I build a nest of beast in my heart. The fang is growling; Kill... Let's go kill. The fang is crying; Kill... Let's go kill. To calm it down, I have no way but slash men..." (translation taken from here)
Although it is mostly exclusive to the series's drama CDs, players can hear parts of it being sung by a woman during his theme song in Samurai Shodown 64.
Genjuro is a brutal warrior who only fights for the pleasure of killing. He likes to dominate over others and hates people who are weak. As such, he has made it his livelihood to take on the dirty business of eliminating targets for just compensation, as he grew up knowing violence and deviance.
There are times when he occasionally feels regretful and shows mercy for his actions; He once let Haohmaru live at Oshizu's pleading. However, he maintains his brutality, counteracting these instances of leniency with more acts of cruelty. Other times, he won't hesitate to be civil with Haohmaru if the situation calls for it, like the old times.
He is often called a "demon" by his victims, usually moments before he slays them. He also enjoys carnal pursuits and gambling, spending the majority of his days cavorting in brothels and gambling dens. 
- Energy Projectile - Genjuro can fire a projectile of energy from his sword.
- Energy Attacks - Genjuro can fuel his sword with ki energy.
- Stun - Genjuro can trap his opponents and leave them completely vulnerable for a limited time.
Though they both trained underneath Nicotine, his fighting style greatly differs from Haohmaru in execution. His fighting stance is one of the few there his back faces towards the foreground as opposed to the other way around, being a bit of an inverse of Haohmaru's stance with his sword pointing more downward in comparison. While his style is rough and wild, Genjuro's is more-likely streamlined and refined to focus on more clean strokes, with slight streaks of brutality (as shown during his connected Hyakki Satsu/Hundred Demons Killer).
All of his special moves are direct references to the Japanese cards known as hanafuda (flower cards) as well as towards a number of games played with the said cards. Depending on whether a move hits or misses, the move will temporarily project the images of a "winning" combo of cards and/or a "miss" based on the featured hanafuda set. His signature special move as one example out of many, the Sanren Satsu (Triple Killing) also has him yell out "Inoshikachō!" (lit. Boar Deer Butterfly) when each hit properly connects, being yet another hanafuda reference only it refers to the card combo in the game Koi-Koi.
His "pet" of sorts is an unnamed orange frog, a reference to the card, Yanagi ni Ono No Tōfū.
His win poses from his first appearance made several heavy references to the deck; his later win poses tone down the references.
- Oni (Demon) - Samurai Shodown II
- Oni no Uta (Demon Song) - Samurai Shodown III
- Oni no Uta - Kai (Demon Song - Modified) - Samurai Shodown IV
- Onibayashi - Samurai Shodown (2019)
- Oni no Uta ~ Beast + Divine Ferocity - Samurai Shodown 64
- Oni no Uta ~ Asura Zanmaden - Samurai Shodown 64-2
- Daimen's Nite Groove (Hot Sake Mix) - Samurai Remix VA (shared with Nicotine)
- Feel It (Mr. Organ Mix) - Samurai Remix VA
- Kong Kuwata - Samurai Shodown II~64 series, Sen, Samurai Shodown (2019); SNK vs Capcom, Neo Beo Battle Coliseum, The King of Fighters: All Star
- Tōru Ōkawa - Samurai Shodown VI
- Kenji Nomura - Samurai Spirits Oni
- Akio Ohtsuka - Samurai Shodown II Dengeki drama CD
- Samurai Shodown II
- Samurai Shodown III
- Shinsetsu Samurai Spirits: Bushidou Retsuden
- Samurai Shodown IV
- Samurai Shodown 64
- Samurai Shodown!
- Samurai Shodown 64-2 - players will only encounter his Bust form as a CPU opponent
- Samurai Shodown! 2
- Samurai Shodown V
- Samurai Shodown V Special
- Samurai Shodown VI
- SNK vs Capcom: SVC Chaos
- Neo Geo Battle Coliseum
- Samurai Shodown Sen
- Samurai Spirits Oni
- Samurai Spirits ~Kengou Hachiban Shoubu~
- Samurai Shodown (2019) (also in SS 64 3D graphics and Puzzle & Dragons Fagan's DLC costume)
- Days of Memories (third and seventh titles) - NPC
- Samurai Spirits - Shimensouka (enemy character)
- Samurai Spirits - Makai Rineki
- SNK’s DARTS: Three In The Black
- Granblue Fantasy
- YAMATO Chronicle
- KOF x Fatal Fury
- Samurai Shodown Online
- Kingdom Story
- Kimi wa Hero
- Samurai Shodown: Oborozuki Densetsu
- Samurai Shodown Tenkadaiichi Kenkakuden
- The King of Fighters: All Star
- Dark Avenger X
- SNK Fighting AGE
- Puzzle & Dragons
- Samurai Shodown: Warriors Rage - passing mention
- SNK vs. Capcom: The Match of the Millennium - in the background of one of the start-up screens
- Voice samples of Genjuro's recruitment scenarios can be heard when the RPG disk is inserted into a music player. This suggests that there were plans to make him a recruitable character at one point in the game's development.
- When asked "The path of the sword is?", Genjuro's response is "A skill for killing people." 
- His favourite type of mate is a woman with strong defenses. 
- Despite popular belief, he has no relation to Iori Yagami.
- He was the character inspiration for the younger design of Shishio Makoto from the manga/anime series Rurouni Kenshin.