Gekisoumaru (ゲキソウマル Gekisōmaru) is the leader of the Swordbot Shinobi Team. Despite the menacing persona he displays to the Predacons—the first his enemies are aware of him is frequently the sudden threat of a flashing kunai—his close friendship with the human Tobio Fūma betrays his compassionate nature.
He can combine with teammates Hishoumaru and Sensuimaru in various configurations. With Gekisoumaru as the top, the combined form is called GoGekisou (ゴウゲキソウ Gōgekisō). After the arrival of Optimus Exprime on Earth, he also gained the ability to combine with Optimus and the Samurai Team leader Kenzan. With Gekisoumaru forming the head, shoulders, and arms, the combined form is called DaiGekisou (ダイゲキソウ Daigekisō). As befits his bestial altmode, his Mini-Con partner is the mammoth-bot Geki.
The Shinobi team were wakened from their stasis in Nagoya Castle when Tobio Fūma activated the Legendisc which Judora and Bakudora were trying to steal. The team confronted the two Predacons, who summoned a team of Jaki to take them on. Though they were no match for Goradora on their own, Tobio activated the Legendisc's power and they were able to form GoGekisou, and eventually brought down the Jaki before striking at the Predacons. With a flash of light, the Autobots and Tobio found themselves in the past where they saw two armies carrying Legendiscs, and then returned to present day, where Gekisoumaru announced that Tobio was now their master.
Gekisoumaru soon revealed that the Shinobi Team had constructed an underground base near Tobio's home. They introduced Tobio to Optimus Prime via video link, and he explained about the Legendiscs. Tobio and the Shinobi Team were subsequently sent back in time to try to obtain the Legendisc held by Kotarō Fūma, however the ninja promptly caught them in chains. They broke free, and when Judora and Gaidora arrived, found themselves again fighting the Jaki. Once Tobio obtained the Legendisc, the Shinobi Team then merged into GoSensui and then GoHishou, before they and Tobio were returned to present day, though without the Legendisc.
The Shinobi Team's research indicated that their fights with the Predacons were causing the Legendiscs to time slip. On their next trip into the past, the Autobots helped Tobio chase off some bandits who were menacing an old man, who turned out to be Sasuke Sarutobi. Sarutobi handed the Legendisc he possessed over to Tobio, and the boy and his Autobot friends successfully returned to present day with it, only to be confronted by Budora, Bakudora, and Dragotron himself. The trio of Autobots were no match for the Predacon leader, however they were suddenly joined by Optimus Exprime.
The Predacons abducted Tobio, and the Shinobi Team merged into GoHishou to give chase. They arrived at Mount Fuji to find the Swordbot Samurai Team was also there as Isami had also been kidnapped. Imbued with the power of all five Legendiscs, Dragotron proved impossible to beat, however Tobio and Isami managed to demerge from him. The two boys had duplicated the power of the Legendiscs, and used it to allow Optimus and the two teams to merge into DaiGekisou. This provided them with enough power to defeat Dragotron and seal the Predacons away once more.
- Gekisou may correspond with 激走, meaning "fast running", while Maru probably corresponds with 丸 ("circle"), a common kanji in historical Japanese names that is still used in period dramas.