Kengo Tachibana/B-Fighter Kuwager (橘 健吾／ビーファイタークワガー Tachibana Kengo/Bī Faitā Kuwagā) is a serious, 22 year old environment investigator. He originally had no respect for Kouhei, because Kouhei was chosen to become Kabuto instead of himself and Kouhei was younger, although they eventually became friends. As Kuwaga (and like G-Stag before him), Kengo donned armor modeled after a stag beetle. At the end of the series, Kuwaga was able to wield the Geist Axe and take control of the giant robot, Kuwaga Titan, which was formerly being used by Descorpion for evil but was not actually evil.