Chiaki Tani is the young man who transforms into Shinken Green, the Samurai of Wood, and appears as a character in the World of Samurai, a dimension visited during Kamen Rider Decade's journey. He is a rebellious and irreverent teenager who initially bristles at the strict traditions of the samurai code, having no interest in becoming a vassal or servant to his team's lord, Takeru Shiba (Shinken Red). This defiance often leads to clashes with Takeru and the more traditional team member, Ryunosuke. Despite his arrogant and selfish facade, Chiaki is cheerful, honest, and possesses a good heart, driven by a genuine desire to protect people and a belief that fighting should be engaging and fun.

Chiaki’s irreverent nature is a product of his upbringing. He lost his mother at a very young age and was raised solely by his father, who encouraged his free-spiritedness and instilled in him a love for martial arts. Unlike the formally trained Ryunosuke, Chiaki abandoned his official training early, making him the least technically skilled fighter in the group. To compensate for this lack of formal power, he relies on his imagination and quick thinking, developing unorthodox tactics and surprise attacks that often catch his enemies off guard and prove to be a significant asset in battle. His hobby of playing Tekken 6: Bloodline Rebellion reflects his strategic mind and competitive spirit.

Within the team, Chiaki shares a strong bond with Kotoha Hanaori (Shinken Yellow), who is also one of the youngest members. He is notably protective of her, becoming upset when she doubts her own intelligence and showing visible discomfort when others express romantic interest in her. He is also the first to accept the eccentric Genta Umemori (Shinken Gold) into the group, bonding with him over their shared free-spirited outlook. While he often butts heads with the by-the-book Ryunosuke, Chiaki deeply respects his skill, and their contrasting approaches allow them to work together in surprising synchronicity. Though he starts as a rival to the leader Takeru, Chiaki gradually learns to respect him, realizing the limits of his own abilities and pledging to one day surpass his lord in skill.

As Shinken Green, Chiaki’s notable abilities are tied to his element of wood. He wields a Wood Spear in combat and uses a personal device called a Shodo Phone to transform. His primary power-up is the Super Shinken Green form, accessed via the Inromaru. In even more dire circumstances, he can achieve the Hyper Shinken Green form. He is often seen wearing casual clothing from American surf and skate brands like Gotcha, a sartorial choice that further distinguishes him from his more traditionally-dressed comrades.