Ankh is the bird-type Greeed who is a dishonest wildcard who sees people for their flaws and is at odds with the other Greeed. Ankh also believes that he has the right to get whatever he wants and detests having to give something away. He was only able to manifest back into existence as his right forearm as he is missing most of his Core Medals; he stole the other Greeed's Core Medals to bolster his own powers. However, he loses one of his Medals when Eiji takes it by accident. Ankh originally intends to force Eiji to return his Medal, only to be saved by Eiji from the Kamakiri Yummy sent after him. In a dire need to see that both of them surviving the Yummy attack, and intending to make Eiji a pawn in his scheme, Ankh saves the human by lending him the OOO Driver and some of the Core Medals he has, enabling him to transform into Kamen Rider OOO. After the Yummy is destroyed, Ankh takes the body of the detective Shingo Izumi who was mortally wounded in the attack, causing Shingo's hair to change color As Ankh explains, he intends to use Shingo's body as a temporary vessel, thus keeping Shingo barely alive, so he could move about unnoticed while feeding on as many Cell Medals as he can to regain his complete form.
While using Shingo's body, he's not only able to control his body but also read his memories. Ankh can remain separated from Shingo's body, but in order to keep Shingo alive, the separation cannot exceed ten minutes. Ankh eventually find himself compromising his original plan, having underestimating Eiji's strength of will and reluctantly cooperates with Eiji to save human lives in exchange that Eiji continue gathering Cell Medals as Kamen Rider OOO. Though Eiji plays him at times, Ankh still prefers working with Eiji over with his fellow Greeed as the human is honest about his motives. Ankh has also developed a liking for popsicles, taking them without second thoughts. He also shows a preference for high places, frequently shown on trees, resting somewhere high in his quarters shared with Eiji, and jumping out of the window instead of going out through the door. Ankh avoids eating poultry due to his connection to birds. Ankh is often seen carrying an iPad or an iPhone 4 to gather information on the current era as well as to keep track on the ownership of the Core Medals. He also receives a gift from Hina in the form of the O Medal Holder to place his Core Medals in. In episode 17, he claims that he cannot create Yummy for an undisclosed reason. He is also unable to fully regenerate his body even after acquiring a total of four Core Medals, only able to project a single rainbow-hued wing from his right shoulder before collapsing in pain.
Hina Izumi is Shingo's sister, who for some reason has superhuman strength, which she is a bit embarrassed about. She began working at the Cous Coussier restaurant as the Greeed awaken, worried for her brother's well being when she eventually learns of the incident he was in. To prevent her from worrying, Eiji sends her a message stating Shingo is on an undercover mission and won't be home for a long time. Eiji later tells her the truth, while promising to save her brother. Eventually, realizing his reason of looking after Ankh, Hina convinces him to work at the Cous Coussier so she can care for her brother's body. She often uses her super strength to keep Ankh in line if he begins to treat her brother's body poorly or when he does something she does not agree with. Ankh does not like her and the two often argue, with only Hina's bizarre strength allowing her to win arguments.
Chiyoko Shiraishi is the owner of the International Cuisine Restaurant Cous Coussier, serving dishes from all over the world. She enjoys cosplaying as a method to bring more customers to her restaurant, frequently changing her restaurant's decor to satisfy different themes. She hires Hina due to her having superhuman strength to lift things around the restaurant, and later Eiji, due to him being a world traveler. She also allows Ankh to stay at the restaurant after Eiji told her that he is a foreigner with a horrible childhood. Later, she also hires Shintaro Goto as a waiter.
The Kougami Foundation is a mysterious organization that has been researching the Greeed ever since they acquired the sarcophagus holding them and the Medals at their Kougami Art Museum. As a result, they developed many Cell Medal-powered items. When the Greeed finally awaken and they realize that Kamen Rider OOO has become active, they begin to assist Kamen Rider OOO in his fight against the Greeed and Yummy.
Kousei Kougami is the president of the Kougami Foundation. Well versed in the history of OOO and the Core Medals, he has anticipated the arrival of the Greeed and has amassed several Cell Medals. He loves baking cakes, commonly birthday cakes, and has built his office over a bakery. He always has a record player in his office usually playing "Happy Birthday", believing that the birth of all things good or bad is a thing of beauty. He also uses strange intonations during his speech, which always shows whenever he becomes enthusiastic about a certain subject, especially when placing emphasis on certain words. Any items he has sent to Kamen Rider OOO typically fit this belief, normally referred to as 'presents' and wrapped up as such. Kougami believes that human desires are the purest and most powerful energy source in existence, so much to the extent of encouraging all around him to succumb to their own desires and do whatever they want. He sees Kamen Rider OOO to be the means to ensure an unlimited supply of energy. To that end, Kougami manages to outwit Ankh into having him and Eiji work for him with a 60% Medal payment for the use his company's gadgets and equipments in order to achieve his life long work. Kousei
Erika Satonaka is Kousei Kougami's personal secretary, often procuring cakes for him. She also goes out of the office to run errands as instructed by the Kougami. Despite being Kougami's usual cake taster, Satonaka actually prefers spicy foods.
Kiyoto Maki is a scientist, one of the Kougami Foundation's finest, having devised the Medal System and placed in charge of the Kougami Biotech Laboratory. He is secretly at odds with Kougami in just about everything, from the ideology and principles they uphold (Kougami's obsession with beginnings vs Maki's for endings) to concrete matters regarding the Medals, like choosing the container for all the Core Medals and who should be the one to use the Birth system. He ultimately decided against going against Kougami's wishes, as Kougami is the one financing all his research. Holding cleanliness above all else, Maki is always seen with his prized puppet "Kiyo-chan", and tends to look at it when he is talking to someone, making it seem like he is instead conversing with the doll. This tendency is so strong that Maki becomes unable to speak properly and loses his normally deadpan composure when Kiyo-chan falls from his shoulder. Maki lacks any empathy for human life and he is more interested with endings and death itself, thus his greatest desire is to see a fitting end to the world. Though he developed Kamen Rider Birth for humans to use Medals like Kamen Rider OOO, Maki was more intent on studying the Greeed. He ironically ends up being studied by Kazari as the two set up a partnership, with Maki finding his suitable ending with the Greeed gaining their Core Medals. During the events of Kamen Rider OOO: Nobunaga's Desire, Maki provides Nobunaga with three black Core Medals, allowing Nobunaga to transform into the Armored Warrior Inhumanoid.
Nobunaga is the primary antagonist of the Kamen Rider OOO: Nobunaga's Desire segment of Kamen Rider × Kamen Rider OOO & W Featuring Skull: Movie War Core. Nobunaga is a Cell Medal-based homonculus created by the Kougami Foundation from the mummified remains of the conqueror Oda Nobunaga and Kougami has Eiji look after him and teach him about the modern world. However, a bug in the computer software used to create Nobunaga causes him to be consumed by the original's desire to rule all of Japan. To that end, Nobunaga uses the powers of three Core Medals (the Sasori Medal, the Kani Medal, and the Ebi Medal) given to him by Kiyoto Maki to become a Greeed-like being called the Armored Warrior Inhumanoid. He also briefly transforms into Kamen Rider Birth before becoming the Armored Warrior Inhumanoid. In promotional materials, the Armored Warrior Inhumanoid was referred to as the "Armored Warrior Greeed".
Yoshino Akechi is a supporting protagonist in the Kamen Rider OOO: Nobunaga's Desire segment of Kamen Rider × Kamen Rider OOO & W Featuring Skull: Movie War Core. She is a senior friend of Hina and a descendant of Akechi Mitsuhide, the legendary samurai who betrayed and killed Oda Nobunaga. She dreams of becoming a professional ballet dancer and Nobunaga falls in love with her because of her dancing. When she breaks her leg, her desire to dance once more is used to create the female Pteranodon Yummy. Nobunaga gives his last energy in order to revive her, until he remembers about how her ancestor, Akechi Mitsuhide, betrayed and killed him and becomes the Armored Warrior Inhumanoid by using the black Core Medals. At the end of the film, it is revealed that she has become a professional dancer.