Koga Saburo (甲賀三郎) is the main character from the classic Japanese fantasy Suwa Engi (諏訪縁起) which was collected in Shintoshu (神道集). He was lost in the underworld which turned his body into a snake. After his return to the ground, he was worshiped as the patron god of Suwa. In some record, Koga Saburo was regarded the same as Mishaguji and Take-Minakata.
"A legendary figure from the story Suwa Engi of the Shintoshu, a collection of stories of gods. He wandered into the underworld and eventually made it back to the surface, becoming a snake in the process. He was eventually worshipped at Suwa Shrine as Suwa Daimyojin. This story is believed to be a variation on Take-Minakata of Japanese lore. In that version, as Take-Minakata, he subjugates Mishaguji, but then is defeated by Take-Mikazuchi. He flees overseas, where he transforms into the snake god there before finding his way back to Suwa."
—Shin Megami Tensei IV Compendium
A demon who was once a member of the defunct Counter-Demon Force, and he is attempting to protect the people and the country in his own way. He has taken over Club Milton in Shibuya, preventing anyone from having Red Pills and disrupting the Ashura-kai's control. So Tayama imposes a quest for Flynn to have him disposed of in exchange for a fellow Samurai's freedom. Believing the prentice Samurai to be Tayama's dogs, he shows no mercy towards them. As he dies, he states he was only protecting the country and that the future is shrouded in mist, and questions humans only to die before he could finish.
His body is turned to stone with his death and Koga's medium is taken by a Ashura-kai member. A Hunter mentions after Koga's death that he was collecting the Reds to prevent humans from turning into demons. The Youthful man mentions before Koga's death that Shibuya had quieted down, but with his death the city will be busy as demons start coming again to get reds. In Walter's route, he is fought once more, revived and turned into a attack dog to serve under Tayama's National Defense Divinities. Koga Saburo expresses gratitude to them for liberating him upon defeat, and asks that they protect the country.
To unlock him for fusion, Flynn must examine the stone that is his defeated remains with the key item, "Ryoja's Scales," in his possession. His medium, along with the mediums for the rest of the National Defense Divinities, are obtained by speaking with the Master Samurai at The Hills building in Roppongi after the alignment lock.
