Ryū Tenkūji (天空寺 龍 Tenkūji Ryū) is Takeru's father and the previous caretaker of Daitenkū-ji. Ten years ago he left on a ghost hunting expedition with his old friends Chikara Saionji and Kenjirō Igarashi on researching the monolith, and came across an Eyecon. Along the way, Ryū discovered the existence of the Gammas from the monolith they've found, and was worried that if they do not hold back on their research, the Gammas will be unleashed upon the world and declares a war against humanity. Before the expedition began, Ryū encountered Edith, as both battled and Ryū is the victor, then finally, he redeemed Edith, and with his knowledge and Ryū's heroic willpower, humanity has a chance to prevent the Gammas' invasions. To prevent a war against Gammas and trying to make a peace with them, just like how Ryū redeemed Edith, Ryū sense an infinite potential within Takeru, to stop Gammas' warring, thus had no choice to involve his son, then also one of his son's friends in his and his colleagues' expeditions, as he believes in Takeru under a promise of his wife before she died during their son's birth. After Saionji betrays them for using Fukami siblings as his guinea pigs for his experiments on opening the monolith's Gamma hole to be able to enter the Gamma World, trapping the youngsters inside, Ryū leads the expedition to try to save Makoto and Kanon Fukami from the Gamma World, but when he fails, he encourages Igarashi not to give up hope in saving the siblings. Five years later, Ryū is killed by a Gamma that has been let loose by Saionji, who turns out to be none other than Adel, leaving Igarashi traumatized. Sometime before his death, he managed to send off the tsuba from Miyamoto Musashi's sword to Takeru and instructs his son to learn about history's greatest heroes. He also ensures that Takeru will be sent the Ore Eyecon upon his 18th birthday. However, the original idea behind this plan was that his own soul would have powered the Ore Eyecon, allowing Takeru to fight Gammas in a duplicate body, but Takeru's death forced plans to change. The fate of Ryū's soul remains in the balance, though, as if Takeru cannot bring himself back to life with the 15 heroic Eyecons within another 99 days, both his soul and Ryū's soul will be lost forever.
During the events of the film Kamen Rider × Kamen Rider Ghost & Drive: Super Movie War Genesis, his death instead happens at the hands of the Da Vinci Gamma, instead of Adel. Later, Ryū's soul fuses with a Ghost Eyecon, transforming it into the Toucon Boost Eyecon which gives Ghost the ability to transform into Toucon Boost Damashii (called in Tousan Damashii in the movie). It is unknown whether this is canon to the TV series. In the TV seris proper, he gives up his soul so Takeru can have a third chance to live by extending his lifespan back to 99 more days in order for his son to find the missing awoken Eyecons, while also giving Takeru the Toucon Boost Eyecon.