Unlike all of the other Riders, the Kamen Rider Hopper Series Riders only have one form that they transform into. Sou Yaguruma was the original TheBee and a 24-year old agent of ZECT. Yaguruma, while TheBee, had his own personal army of ZECT Troopers called Shadow, which had yellow stripes on their uniform, indicating that they are an elite unit of ZECT Troopers. He is a perfectionist and brilliant tactician, when he's calm, he's a caring person who possesses a strict code of teamwork and demands perfection. However, he's also impulsive, brash and quick to anger. This one flaw played a part in his falling out when Tendou managed to infiltrate his flawless security team and upstage him by revealing how a Worm had done the same, challenging Kabuto to a fight to kill him. Though he defeated Tendou and destroy his belt, he snaps when Tendou later transformed with a repaired belt. His resulting mental state caused him to disregard the safety of his team in favor of getting revenge against Tendou, which led to his Zecter rejecting him and being transferred out of Shadow. After this he was reassigned to another part of the city, he learned that the members of his former team were being eliminated from within by a traitor.
Despite his renewed vow to protect his team, Kageyama was made the new TheBee and new leader of Shadow, turning his back on his former superior. After a series of unknown events, Yaguruma returned as a very different person with a new outfit. He saw himself as a "loser" unworthy of his previous ideology and embraces a new ideology around hell and darkness. After bringing Kagayama under his wing once more, Yaguruma attempts to stir his partner on to see things as he does, seeing that Kageyama only setting himself up for a fall at the slightest glimmer of hope while expressing a bit of envy because he could no longer feel any emotion. As either TheBee or KickHopper, Yaguruma uses a fighting style themed around kicking attacks, but as Kick Hopper, he meets every attack with an attack of his own rather than a traditional block or parry. After destroying multiple Pupa Worm, Yaguruma quickly stripped Kageyama of the TheBee Zecter with a Rider Kick after telling him that he had "been to Hell" and attempted to invite Kageyama to come with him.
Though Kageyama is reluctant at first, he accepts Yaguruma's offer when he saved his life, providing his partner with a Hopper Zecter of his own. The two Hoppers easily defeating Kabuto and Gatack after the two were weakened by the activation of the 'Red Shoes' system. He and Kageyama attempt to destroy a confused and weakened Rena Mamiya. However, he hesitates at the last moment, as if showing affection for Rena when he sees in her eyes that she has gone through the same darkness as he. Drake and Rena are then saved by Gon. Their plan resulted in a recovery of Rena's Worm memories. When asked by Kageyama later, he says that he has indeed taken a liking to Rena, and therefore didn't kill her. Even more so, Yaguruma protects Rena from Subst Worm when she is endangered. Later, in his encounter with Rena and Daisuke, when Yaguruma says to Daisuke that he will protect Rena, he gets surprised when Rena, who temporarily reverted back to Uca Worm, hit him hard which sent him flying away. After that, he shows up with an injured face to a laughing Kageyama and their bond is restored.
After defeating Tsurugi, Yaguruma offers him a place as his little brother, which Tsurugi happily accepts. Yaguruma meets Tendou once more, and challenges him to a tofu cook-off, but since the seller is sold out, they would have to reschedule. The trio then encounters Reiji Nogi who makes short work of them using "Freeze" to move out of the way and cause all their Rider Finishers to collide. Tendou accidentally stood them up, and Yaguruma and Kageyama are left in the street wondering if Tendou will come and if the challenge will still commence. The TheBee Zecter is once again offered to him by Tadokoro, but he declares that he is enjoying his stay in the pitch black hell, as he kicks the case containing the Zecter. Kageyama and Yaguruma watch as Reiji Nogi advances into Area Z, and Kageyama wants to help them fight. But later after meeting with Tendou and Kagami as they prepare to face Cassis Worm, he decides to help them as Cassis Worm Gradius defeated Kageyama (who went and fought earlier as TheBee for the last time) and Gatack. They perform a Triple Rider Kick and effectively neutralize his 'Absorb' ability.
Yaguruma later laughs at Kageyama for straying from the path of darkness and becoming TheBee, and so Kageyama returns to him, as Punch Hopper once again. Yaguruma and Kageyama bind themselves with chains and weights so that they would not be able to fight for justice. Ignoring Tendou's request for assistance, he along with Kageyama sit and meditate, attempting to regain their darkness. After seeing a picture of the Northern Lights, Yaguruma begins to ponder returning to the light again. Upon seeing Kageyama with a Worm identification necklace, Yaguruma scolds him for using such a device (apparently aware of its effect on humans). Yaguruma realizes that Kageyama has become a Native Worm and can no longer control his form. As a show of pity, he uses a Rider Kick to end Kageyama's suffering. Holding his fallen partner, Yaguruma looks up to the stars in the night sky and says that he and Kageyama will always be partners and that they have to regain the light once again.