Before joining the Mafia, Genkishi was a swordsman unfortunate enough to receive an incurable disease while traveling. While in treatment, he was visited by Byakuran, who cured him using his knowledge gathered from his trips into other parallel worlds. In response, Genkishi came to know him as a god. Genkishi later joined the Giglio Nero Famiglia and acted as a spy for Byakuran during the war against the Gesso Famiglia. A ceasefire was agreed if Genkishi could defeat a powerful swordsman for the Gesso. However, Genkishi used illusions to fake his defeat so that he could kill the remaining Giglio Nero and steal their Mare Rings when their guards were down. However, their leader Uni saw through this and held him back; thus, in order to stop further bloodshed, Uni agreed to meet Byakuran. As a result, Byakuran drugged Uni to dull her heart and take away her power of speech, also forcing her to agree to the joining of the Gesso and the Giglio Nero.
During the war between the Millefiore and Vongola, Genkishi was sent to Namimori in order to protect Shoichi Irie at Merone Base. During the Vongola's invasion of the base, Genkishi was positioned to intercept Lal Mirch and Takeshi Yamamoto, who he swiftly defeated. However, before he could kill them he was interrupted by Kyoya Hibari. Genkishi came inches from killing Hibari in battle but Hibari was at that moment switched with his past self and joined with the rest of the Vongola. After being separated from them, Genkishi fought Tsunayoshi Sawada and unleashed the power of his Hell Ring. However, he held back, as Tsuna's eyes reminded him of Uni's, and escaped after his defeat.
During Choice, Genkishi (disguised as Torikabuto's subordinate, Saru) was chosen as the second Mist member of the Millefiore side. After the Vongola deployed flame decoys the Millefiore decided to destroy each one in order to find the real target.
Genkishi then encountered Yamamoto and, after Genkishi revealed his true identity, the two fought for a second time. However, even after using his Hell Ring, Genkishi was defeated by Yamamoto's Cambio Forma, Ugetsu Asari's Four Irregular Swords. Kikyo (on orders from Byakuran) then released a number of Bellflowers into Genkishi's Armatura that began killing him from within. Genkishi then died, still adamant that Byakuran would save him.