SaiDain is the Geki Beast of Ken Hisatsu/GekiChopper. It is considerably larger and possesses more brute force than the other GekiBeasts and can also unify sets of Gekibeasts to amplify their attacks. When SaiDain first appeared, it caused a rain of Beast Power Bloom, which multiplied the energies of GekiJyuken and RinJyuken alike tenfold.
During the GekiRin rebellion, JuKen's founder Bruce E was bretrayed and murdered by three of his students who would go on to become the Kenma of Rin JyuKen Akugata. After the Kenma were defeated and their souls inprisoned in the Kenma Bracelet, ShaFu and the other Kensei learned that their master's soul still remained and used the Sozyuto to carve a totem for it out of rock. Years later, the Sozyuto was entrusted by the Kensei to Ken only to have it stolen by Mele who gave it to Rio so the two of them could enter Jugenkyo and take Bruce E's power for Rio's use. The GekiRangers and the Kensei followed them and during the battle, Ken was able to reclaim the Sozyuto and with it, the awakened SaiDain as his personal GekiBeast.
In addition to it's beast form, SaiDain can transfrom into a humanoid version, SaiDaiOh, (Great Rhino King). In this form, SaiDain's horn becomes the SaiDaiKen (Big Break Sword) and its back becomes a shield. For its finisher, SaiDaiOh focuses Geki Hard Kensan into the SaiDaiKen and then slashes the opponent in the form of JuKen's symbol.
Herculean Giant SaiDaiGekiFire
SaiDain can combine with GekiGorilla to form the centaurish SaiDaiGekiFire (サイダイゲキファイヤー, SaiDaiGekiFaiyā), with GekiWolf riding its shoulders and GekiGazelle and GekiPenguin running alongside it. In this form, SaiDaiGekiFire combines the energies of Kageki (the main Gekirangers), Shigeki (GekiViolet), and Geki Hard Kensan (GekiChopper), into its attacks. It's finisher is Fire Break Big Assault where SaiDain knocks the opponent into the air with a double slash of its horn where GekiWolf, Cheetah, and Jaguar attack it in turn before GekiGorilla finishes it off with its double swinging fists.
Beast-Fist Giant SaiDaiGekiTohja
GekiTiger can also combine with SaiDain to form SaiDaiGekiTohja (サイダイゲキトージャ, SaiDaiGekiTōja), with GekiWolf on its shoulders and GekiCheetah and GekiJaguar running alongside him. It's finisher is almost the exact same as SaiDaiGekiFire.
Beast-Fist Giant SaiDaiGekiRinTohja
The final combination of GekiBeasts and RinBeasts as bond. It used finishing attack SaiDai-Geki-Rin Slash (砕大激臨斬 Saidai Geki Rin Zan) to defeat Long.