Tsurugi Kamishiro is a 20-year old man and descendant of the Discabil family of England. He lives in a gorgeous European-style building with his butler Jiiya. He is good at sports, art, study, and many other skills, and has been seen to be able to understand and speak French, Chinese, and Italian in addition to English and Japanese. He always calls Kagami his friend and Misaki as "Misakinu". Tsurugi wants to be the man who is best at everything. Unlike Souji who quotes his grandmother, Tsurugi quotes his butler, Jiiya instead. Tsurugi is also as arrogant as Souji. He was almost killed on the spot by a SalisWorm, when he was told to put his seat belt on, and Tsurugi's failure to look before crossing a street resulted in an accident in which Souji's sister Jyuka to get hurt, and as the cops scorned him, he told them that the car carrying Jyuka should have gone ahead and Souji punched him for getting Jyuka hurt. He had an older sister named Mika who was killed by Scorpio Worm, and suffers nightmares as a result. The fact that Mika was killed near a field of red roses also sparked a disdain for roses.
He has been employed to ZECT in exchange for the reward, but the monetary part of his contract was annulled when the Gatack system was first utilized. He aids Kabuto after he helped him realize that his butler Jiiya, was teaching him to be a better person now utilizing what his mentor taught him: that a noble act must be nobly returned. In truth, Tsurugi was killed on the same day as his sister by Scorpio Worm. Moments before his death, Scorpio Worm choose to mimic him. Through impossible odds however, Tsurugi's arrogant nature and personality overpowered Scorpio Worm's own, leading him to believe he was in fact Tsurugi Kamishiro, completely unaware of his Worm identity or that he had killed his sister. Jiiya later revealed he had been aware of his master's true identity, but believed it best to withhold the information in the hopes Scorpio Worm would never regain control and his master would continue to exist.
Tsurugi came into contact with the Sasword zecter and accepted his role as Kamen Rider Sasword with the goal of exterminating every last Worm. Tsurugi has only recently learned (from both Gon and Jiiya) that the Discabil family fortune is no more, and this confounded him deeply, so he worked hard to rebuild it and worked at the Soba shop where Misaki always visit. He has a crush on her, to which she feels annoyed. Tsurugi meets the Worm who mimics Misaki (without him knowing the truth) and they enjoy a dance together. Uca Worm intervenes and defeats Sasword. Before she moves in the killing blow, the Misaki Worm saves him, which leads Tsurugi to realize her real identity. Later on, Tsurugi meets the Misaki Worm again and hands her his sister's red shoes. But for reason unknown, Misaki Worm attacks and scratches Tsurugi's face. Tsurugi reacts by stabbing the Sasword saber through Misaki Worm, killing her while saying that he won't forgive any Worm.
Tsurugi sold his Sasword saber and Zecter to Tendou, but Jiya tells Kagami that without the Sasword Zecter, Tsurugi will surely become Scorpio Worm again. Kagami tries but ultimately fails in the end as Tendou defeats him. Tsurugi did this to help rebuild his Discabil family and he still has the legendary sword 'Discalibur' passed down from generations. When Tsurugi engages three Worms with it, he discovers that the sword is actually just a grip with no blade. The real sword was sold earlier to clear some debts of the family. However, Jiiya arrives in time to deliver the real sword to Tsurugi, which he uses to kill the Worms easily. Unfortunately for Tsurugi, the Discalibur is re-bought using the money for selling the Sasword Zecter and the money is not enough for it. Tsurugi begins to go on journeys to learn about the common people's happiness because he must stand at the top of being 'common.'
At first he dresses as a school boy for a day and experiences life in a different way, and although not his original intent, he realizes that the world does indeed contain good people after meeting Jyuka. Tsurugi enters Jyuka's school. Due to school policy, Jiiya was forcibly dragged out of the classroom many times to prevent him from helping Tsurugi. Tsurugi is also able to transform into Sasword again as he has retrieved his Sasword saber from Tendou. Despite being able to call on the Sasword Zecter, the Perfect Zecter can still summon the Sasword Zecter when Hyper Kabuto calls for it, which led to an infuriated Tsurugi. After Tsurugi realized that his love for Misaki would never be, he decided to do his best so that Kagami and Misaki would be happy together, unknowing that their love was just a setup. He sets Kagami and Misaki on a date. Unfortunately, after meeting Misaki again and discovering that she and Kagami are not a couple, Tsurugi is captured by the Hopper Riders. He was challenged and lost, receiving a Rider Kick and Punch to the head. He is then tricked into thinking that the Hopper Riders darkness is good and so he joined them.
The trio then eventually encounters Reiji Nogi who makes short work of them using "Reflect" to cause all their Rider Finishers to collide to each other. Abandoned by the Hoppers after fighting Nogi, Tsurugi begins to fall apart, but after Tendou tells him he does not see Misaki for who she is, but rather his sister, he realizes that he needs to accept her for herself. Refilled with spirit, he is able to convince Misaki to also see him for who he really is. When Misaki is attacked by Cassis Worm Gladius, Tsurugi came to rescue her, attacking the Worm with his Rider Slash. However, Cassis Worm Gladius absorbed the power of the finisher and used the absorbed power against Sasword, damaging both Misaki and Tsurugi. Tsurugi finally proves his worth by defending Misaki from an onslaught of attacks from Nogi, at the risk of his own body. Finally defeated, Tsurugi lies in shock as Misaki promises to accept him for who he is. Tsurugi's assistance is also requested by Tendou in order to fight the massive onslaught of Worms, and so he joins ZECT and is given his own team of ZECT Troopers. However, he used them for the sole purpose of protecting Misaki, going so far as to dive into a river to find her missing shoe. Eventually however, his troopers abandoned him, saying it isn't worth it and they'd rather fight Worms. On his way to his date, Tsurugi runs into Cassis Worm Clipeus who he does battle with. After being defeated, Tsurugi loses control of his body and once again becomes Scorpio Worm. After meeting Misaki and transforming into Scorpio Worm once, he is able to revert, but he does not know of his transformation. Clipeus appears again and forces another transformation, in turn causing Tsurugi to realize that he is indeed a Worm.
After ripping up the scarf he made for Misaki and shouting at Jiiya, Tsurugi abandons hope and seemingly begins on a quest to destroy all Riders and be at the 'top of the Worms.' Both Cassis and Clipeuses Worm attempted a partnership with Scorpio Worm, but Tsurugi outright refuses and tells them he's taking charge. With that, he attacks both Clipeuses, having them become his servants after overpowering them and telling them to gather all of the Worms under him. After having Kagami kidnapped, Tendou is sent a note saying that he must hand over all the Zecters or Kagami will die. As Tendou hands over the Zecters, Misaki appears along with massive amounts of ZECT Troopers, allowing enough time for the Zecters to escape after seemingly crushed but actually receiving no damage at all. During the ensuing battle that took out most of the Worms, as he truly intended from the start, Tsurugi allows Tendou to destroy him so that his wish of all Worms being destroyed and vengeance for his sister may be granted. Back at his mansion, a dying Tsurugi sat on an old wicker and asks Jiyia if it's okay for him to dream, Jiiya promises that he will always be by his side. Hearing those words, Tsurugi dies. During the epilogue, a restaurant is named in his honor, being run by both Misaki and Jiiya.