Tōsei Kaneshiro is the main antagonist of The One Who Shines in the Darkness. He presented himself as the humble owner of a local steakhouse; he's secretly the master of the Madō Horrors within Volcity. He's the fourth illegitimate son of Kensui Kaneshiro and quietly manipulated terrible events in the shadows; he would later take over Kaneshiro Corporation and commanded SG1. After his plans were foiled, he became a horror and was slayed by Ryūga Dōgai and Rian.
Tousei is the fourth illegitimate son of Kensui Kaneshiro. Although it was a fling, Tousei claimed Kensui raped his mother and denied him of his existence. Tousei led a hateful and resentful life. While his mother filled him with notions of becoming a great man, Tousei saw his mother as a whore for being an escort to rich men. Things changed when he came upon the scrolls detailing Zedom. Tampering with dark forces, witnessing the power of a Horror first hand, Tousei figured a means to get his revenge against the Kaneshiro family by creating his own private army of Madou Horrors to infiltrate and control major operations of the Kaneshiro business. Being a manipulator by nature, Tousei prefers others to do his dirty work. Furthermore, as seen during Zedom's rampage and his last moment as a human and then as a Horror, Tousei is nothing more than a coward who would weasel out of danger by any means. Though a normal human, his blood relation to a former Makai Priestess allowed Tousei to be well-informed of the Makai realm.
Tousei was born as the result of Kensui Kaneshiro, Vol City's founder, having a short-lived affair with his mother Karen. An exiled Makai Priestess, Karen raised Tousei with the intent to become a man of power. With that mindset, learning of the legend of Zedom from a chest in an abandoned house of his maternal family, Tousei deliberately brought a Inga Gate to his home with the emerging Horror possessing his mother and devouring her guests before his eyes. Only able to escape death by the Inga Gate's barrier, the event aroused Tousei and he desired to make use of the Horrors' power.
Fifteen years prior to the events of Garo: Yami o Terasu Mono, having found the ruins under Vol City, Tousei ventured to the Hill of Zedom's Arm to capture one of the one of the Makai Priestess there while using a Madō Horror Plant to convert Sonshi into his first Madō Horror follower. From there, Tousei confines Hakana beneath the Hill of Zedom's Head under Vol City to have her germinate Madō Horror Plants so he can sire Madō Horrors while taking over Vol City from the shadows under the guise of the owner of the Steak House restaurant. Among his victims was his half brother Kaga Kaneshiro, rendering him mute before driving him off into the graveyard.
Upon learning of Ryūga Dōgai's arrival in Vol City, Tousei developed an interest in the Makai Knight and, taking advantage of being suspected of a recent chain of terrorist attacks to get close to her, converts Enhou into a Madō Horror. From there, Tousei tricks Ryūga into thinking his father is responsible for Vol City's predicament in order to get close enough as an ally to convert him into a Madō Horror. But upon seeing the Garo armor's brilliance intensify, Tousei decides to let the Makai Knight be and use his lesser minions to speed up the armor's maturation while ending the song of the goddess to obtain the final Madō Horror Plant.
Once his cover is unexpectedly blown by Kensui, Tousei decides to take full control of the Kaneshiro Group by having Enhou and Rivera kill off his remaining siblings and their families so he would be the sole remaining heir. After giving his father his goodbyes while having Sonshi devour the old man, Tousei uses his new power as head of the Kaneshiro Group to have SG-1 frame the entire Makai Knight group in the city for the 15 murders. Though he had the advantage on the Makai Knights as they can not kill a normal human, deciding to go through with it despite the Garo armor still not matured, Tousei's scheme to convert Ryūga with the final Madō Horror Plant fails.
Despite the setback, Tousei has Rian captured so she can germinate a new batch Madō Horror Plants for him from the seeds contained in Zedom's head. However, the plot fall apart when Zedom is unexpectedly revived and both Enhou and Rivera are killed off by the Makai Knights. With only Sonshi left, Tousei is forced to flee from his lair when Zedom begins decimating the ruins. After Sonshi is spirited away from him, watching the Makai Knights and Rian venture back to the ruins to fight Zedom, Tousei attempts to leave the city by using a group of SG-1 troopers transporting Hakana's body as his bodyguards to hold off the Horrors that are now running rampant. Unfortunately, expecting the monsters would target the SG-1 instead of himself, Tousei failed to realize the countless number Horrors would ignore the troopers and go after him directly due to his vast inner darkness. Cornered in the restroom, Tousei ends up becoming a host to the large number Horrors and is forced to go into hiding after Zedom is destroyed and everyone's memories of the events are altered. Resuming his steakhouse guise, Tousei finds himself visited by Ryūga who intends to finish off the loose end now that he is a Horror. Though he attempts to run, Tousei is blocked by Rian who proceeds to torture the coward before putting him out of his misery with the thought of every person he has wronged in her thoughts.
Despite his death, Tousei's actions greatly haunted Ryūgā after he moved to Line City. Although he managed to find the closure following Volcity incident, Ryūgā becomes enraged when Vestage emulated his crimes by distributing objects tainted with Inga all over the city, so much that he angrily called the Horror out for it despite being surrounded by potential Inga Gates in process. Before he could slay the Horror however, his would be strongest nemesis appeared and devoured Vestage after the latter outlived his usefulness to him.
- Restaurant Owner: Tousei owns a Steakhouse and does everything on his own. Suggestively, he mastered how to run his own restaurant and do it all on his own without help.
- Makai Knowledge: Acquired from the tomes left behind by his mother Karen, Tousei used his mother's chest to help him understand the culture of the Makai Order, magics, and lore of their world.
- Zedom's Seedling: Tousei had a collection of seedlings that made his personal army of Madō Horrors.
- Sedatives & Drugs: To get what he wants, Tousei often uses sedatives and drugs to manipulate things in his favor. He has used sedatives to temporarily distract people long enough for him to turn them into Madō Horrors and drugs to force less cooperative people to
- Tousei Kaneshiro is portrayed by Kanji Tsuda who also portrayed Kengi.
- Tousei is one of few main antagonists who wasn't fought by the protagonists of the franchise, let alone having notable combat skills.
- Tousei's character as a human antagonist who control a batch of Horror thralls would later inspired Ashiya Dōman and Mendoza in Anime Series. the difference was the latter two possess formidable fighting skills that made them formidable opponents even to Makai Knights who bear the title of Garo.