|Name: Sakuya Tachibana|
|Designation: Kamen Rider Garren|
|Weapons: Garren Rouzer|
|Gear: Garren Buckle, Rouse Absorber, Red Rhombus|
|Tachibana was originally a researcher of the Humanity Foundation who graduated from the Sazahaibu University and was selected to be the user of Rider System 01 after Go Kiryu was found to be incompatible with the system. Tachibana begins to suffer a form of cellular breakdown with only sealing the Undead slowing down the process. Combined with his feelings towards Kenzaki being his backup when he can't manage it, he blames Karasuma for his condition. When he attempted in vain to seal the Locust Undead, he is forced to abduct Karasuma just prior to the Undead attacking BOARD. Though he intended to get the answers he needs, Karasuma was in coma and put on life support with Tachibana safeguarding him until Hirose finds him. Though he leaves Karasuma in her care, it only revealed that it was only a decoy.
After his doctor and dear friend Sayoko Fukasawa relays Karasuma's message, that his subconscious fear is causing the breakdown, Tachibana encounters the Peacock Undead, who personally attempts to retrieve him for his Leangle project. After escaping Isaka, Kotaro manages to talk Tachibana not to let his fear control him though Tachibana denies that. He arrives to save Blade, however Garren's fusion rate goes down during his fight with the Trilobite Undead. After being saved, Tachibana begs Karasuma for a means to be free of his fear, but Karasuma say he can't. Though Tachibana attempts to resume a normal life by dating Sayoko, the Zebra Undead forces him to reveal himself as a Rider in front to Sayoko before fighting the Undead and Blade arrived to aid him. In spite of Sayoko asking him to go off with her, Tachibana turns her down. While at BOARD's original, Tachibana battles the Peacock Undead and takes him with intend to have Tachibana work for him by removing of his fears with exposure to the Schuld Kestner seaweed, an extinct plant that intensifies the aggressive nature of the subject.
Although he became more aggressive and worked under Isaka for more of the seaweed, Tachibana was unaware of the eventual damage it would do to his nervous system. Even though Sayoko warned him in vain, Tachibana shrugged it off until he learned that Isaka murdered Sayoko for meddling in his affairs, defeating the Peacock Undead and sealed him. Later, as his way of repenting for being maniplated by an Undead, Tachibana takes Mutsuki under his wing. He later came face to face with the Category King of Diamonds and battled it out with him. The Undead told him that if he was sealed, Joker would be declared winner and that all of humanity would suffer because of his choice. Garren answered that he believes in his friends. The battle ended with Garren nowhere to be found and the King Undead sealed leaving the Joker as the winner. Tachibana is found upon the arrival of the Chief telling Kenzaki that he was saved because of him.