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Official Site: Bandai

is the primary and eponymous protagonist of the 2009–2010 Kamen Rider Series Kamen Rider W. Kamen Rider Double's name is taken from the English word double as he is the first Kamen Rider that requires two people to transform, and his motif is that of the letter W. His debut was a cameo in the film Kamen Rider Decade: All Riders vs. Dai-Shocker where he faces off against Shadow Moon.

is a self-proclaimed "hardboiled detective", though considered "halfboiled" by all others around him to his chagrin. He dresses in the style from the 1940s and wears a black fedora/trilby made by the Windscale design house. He has a sharp intuition and may even figure out the culprit behind a crime before having Philip confirm his or her identity. Vowing to ensure that no one ever feels sad, Shotaro took on the job as the protege of Futo's private investigator Sokichi Narumi after admiring his work as a child. However, during the incident, an investigation into a mysterious organization led to Shotaro meeting Philip prior to Narumi's death, leaving Shotaro to continue in his stead, Narumi passing on his white fedora to Shotaro, his final words telling Shotaro to "grow into a man worthy of wearing it". A year later, refusing to let his mentor's death be in vain, Shotaro works to stop the Dopant crime wave by being the man on the street, contacting his various informants and transforming into Kamen Rider Double by providing his body for the formation. Shotaro takes the role of Kamen Rider Double very seriously and with great pride as the name "Kamen Rider" was given to them by the citizens themselves. As such, he tries hard to make a good name for Kamen Rider Double. Shotaro's body, however, was never meant to handle Gaia Memories and he was never the one intended to be partnered with Philip, which is why he initially had trouble maintaining their Rider form when Philip's power was evolving. However, he proved to be able to overcome these obstacles to become worthy of being the true Kamen Rider Double. Another goal he has throughout the series is to live up to Narumi's expectations, which he finally does in the battle with the Utopia Dopant. During the battle, he wears Sokichi Narumi's white fedora, having finally believed in himself that he had become worth of wearing it.

In the movie Kamen Rider W Forever: A to Z/The Gaia Memories of Fate, Shotaro receives his mentor's Lost Driver. With the T2 Joker Memory, Shotaro can become allowing him to fight on his own. Before Philip becomes one with the Earth after saving Wakana and defeating the Utopia Dopant, he came across the Lost Driver and gives it to Shotaro as a farewell gift, allowing Shotaro to continue fighting as Kamen Rider Joker after his disappearance using the standard Joker Memory. About a year later, Shotaro continues to fight doing the best he can to protect the city of Futo when a gang of kids calling themselves EXE becomes a threat. However, he is soon reunited with Philip as they, once again, protect the city as Kamen Rider Double.

His surname is literally translated as and his Gaia Memories provide the left side of any Kamen Rider Double formation.

Kamen Rider Double has not been a contender in any CBUB matches.