As a special anniversary series, Kamen Rider Zi-O features cameos from actors reprising their roles from past Kamen Rider series. While most appear in one or two episodes and movies, the protagonists of Kamen Rider Decade become recurring characters as they are directly involved in Kamen Rider Zi-Os storyline.

Kamen Rider Build Sento Kiryu , born , is a scientist and the titular Rider of . Originally from an alternate reality where the alien Evolto divided Japan into three regions, Sento caused his reality to be absorbed into the "prime" Kamen Rider universe after using the Pandora Box to erase Evolto's existence from Earth's history.

Due to the Another Rider Another Build's creation, Sento lost his memories as Kamen Rider Build until Sougo Tokiwa came to seek his help, causing the Build Ride Watch to appear in Sento's pocket and restore his memories. Sento gave it to Sougo before the latter and his ally Geiz travel back to the former's world in 2017 to defeat Another Build's past iteration, establishing a bootstrap paradox in the process.

Year 2017: Sento encounters a time-displaced Sougo while he and his ally Ryuga were still in their reality, deducing the boy came from the future. They would encounter Sougo again, this time with Geiz, as the four of them fought Another Build together. During the fight, Sento gradually loses his powers and memories as a Kamen Rider, to the point where he started referring to himself as Takumi. To prevent Sento's past from being permanently altered, Sougo gives him and Ryuga blank Ride Watches so they can connect with him in the future.

During the events of Kamen Rider Heisei Generations Forever, Sento and Ryuga help Shingo Hisanaga escape from Another W and encounter the Super Time Jacker, Tid before joining forces with Sougo and the other Heisei Kamen Riders to defeat him.

reprises his role as Sento Kiryu.

Ryuga Banjo Also returning from Kamen Rider Build, is a former professional fighter who can transform into . Like Sento, he was originally from an alternate reality before Sento merged it with the "prime" Kamen Rider universe.

Due to Another Build's creation, Ryuga lost his memories as Cross-Z before Sougo came to seek Sento's help, causing the Cross-Z Ride Watch to appear in Ryuga's pocket and restore his memories. Ryuga gave it to Sougo before the latter and Geiz travel back to Ryuga's world in 2017 to defeat Another Build's past iteration.

Year 2017: Ryuga encounters a time-displaced Sougo in 2017 while he and Sento were still in their reality. They would later meet Sougo again, this time with Geiz, as the four of them fought Another Build together. During the fight, Ryuga gradually loses his powers and memories as a Kamen Rider, but Sougo gives him and Sento blank Ride Watches so they can connect with him in the future.

During the events of Kamen Rider Heisei Generations Forever, Ryuga and Sento save Shingo Hisanaga from Another W and encounter Tid before joining forces with the other Heisei Kamen Riders to defeat him.

reprises his role as Ryuga Banjo.

Gentoku Himuro Also returning from Kamen Rider Build, is the son of Touto's prime minister Taizan as well as the former leader of Faust and head of the Touto Institute who can transform into the first and later .

During the events of Kamen Rider Heisei Generations Forever, Gentoku temporarily recovers his memories and powers before joining Kazumi to assist Sento and Ryuga in combatting Another W and joining the Heisei Kamen Riders in their fight against Tid.

reprises his role as Gentoku Himuro.

Kazumi Sawatari Also returning from Kamen Rider Build, is the owner of the Sawatari farm who later became a soldier capable of transforming into .

During the events of Kamen Rider Heisei Generations Forever, Kazumi temporarily recovers his memories and powers before joining Gentoku to assist Sento and Ryuga in their fight against Another W and joining the Heisei Kamen Riders in their fight against Tid.

reprises his role as Kazumi Sawatari.

Misora Isurugi Also returning from Kamen Rider Build, is the daughter of Sōichi Isurugi and ally of Sento's who was temporarily possessed by the Martian Queen Vernage.

During the events of Kamen Rider Heisei Generations Forever, Misora temporarily recovers her memories and assists the Heisei Kamen Riders in their fight against Tid.

reprises her role as Misora Isurugi.

Kamen Rider Evol , , was a sociopathic alien who possessed Soichi and assumed the identity to further his goals of destroying the Earth before he was eventually defeated by Sento and his allies.

After the Build Ride Watch was destroyed, an alternate reality version of Evolto was brought to Sougo's world to join Swartz's forces. While he managed to defeat Grand Zi-O, Evol was destroyed by Ohma Zi-O.

Instead of being vocally reprised by or physically reprised by Isurugi's actor , Kamen Rider Evol appears in a non-speaking role.

Kamen Rider Ex-Aid Emu Hojo , a young doctor, genius gamer, and titular Rider of .

In 2018, he initially attacked Sougo and Geiz after mistaking them for enemies before losing most of his memories of being Kamen Rider Ex-Aid due to Another Ex-Aid's creation and giving the Ex-Aid Ride Watch to Sougo.

Year 2016: Encountering Another Ex-Aid, Emu transforms into Kamen Rider Ex-Aid and assists Sougo and Geiz by fending off the Bugsters summoned by his twisted counterpart until his powers faded away before witnessing Sougo transform into Kamen Rider Zi-O to defeat Another Ex-Aid. Emu is then given a blank Ride Watch to connect with Sougo in the future.

reprises his role as Emu Hojo.

Hiiro Kagami Also returning from Kamen Rider Ex-Aid, is a young prodigy surgeon who can transform into .

When Sougo and his friends sought out Emu to stop Another Ex-Aid from kidnapping young boys in search of a heart donor for his ailing son, Hiiro was suspicious of their intentions. He later reveals that the boy could have been cured had he been brought to him before he reached the transplant stage. Thanks to Sougo and Geiz's actions in the past, Hiiro was able to cure Iida's son of his heart condition.

reprises his role as Hiiro Kagami.

Kuroto Dan Also returning from Kamen Rider Ex-Aid, is one of the orchestrators of the Bugster virus outbreak and the second CEO of Genm Corp. who has a God complex and can transform into .

After the events of Ex-Aid and Genm Corp.'s existence were erased following Another Ex-Aid's creation, Kuroto became a game developer for who was pressured by his perfectionist father until the Time Jacker Heure transforms him into . Within the span of eight years, Kuroto killed his father, established the mega-corporation, and proceeded to create an independent nation as . He also kept Eiji Hino and Hina Izumi imprisoned before Sougo freed them by posing as Kuroto's royal guard. While Geiz distracted the present Another OOO, Sougo and Tsukuyomi traveled back in time to defeat the Another Rider's past self.

Year 2016: As Another OOO, Kuroto committed patricide to usurp his father's position as the CEO of Dan Corp. before facing Geiz with the Genm Armor. However, since it was not the date of his creation and Geiz unknowingly used the wrong Ride Watch, Geiz was forced to retreat as Kuroto revived from his destruction. Year 2010: In the middle of his writer's block, Heure transforms Kuroto into Another OOO. However, Sougo appeared after the fact and defeated him with the OOO Armor.

As Another OOO, Kuroto has hawk-like wings for flight capabilities, tiger-like claws for slashing enemies, and grasshopper-like legs for superhuman jumping. Using Cell Medals, he can create or transform people into Waste Yummies. Additionally, he was in possession of the Genm Ride Watch through unknown means until he dropped it when the Taka Watchroid attacked, which Geiz claimed for his own use.

reprises his role as Kuroto Dan.

Masamune Dan is the original CEO of Genm Corp. and the father of Kuroto Dan. In the original timeline, he is the mastermind of the Kamen Rider Chronicle MMO project as well as the first and second Bugster outbreaks who can transform into .

As a result of the Time Jackers' actions, Masamune retained his position as the CEO of Dan Corp. However, his obsession for Kuroto to become successful resulted in his death in 2016 after his son usurped him moments before Geiz and Tsukuyomi arrived too late in an attempt to prevent it.

Instead of being reprised by , Masamune Dan is portrayed by an unidentified stand-in while photos of his original actor appear within Sougo's Time Mazine so he could track the chronology of Kuroto's rise to power.

Kamen Rider Lazer , a.k.a. , is one of Emu's allies in the fight against the Bugsters' outbreak.

During the events of Heisei Generations Forever, Lazer aided Ex-Aid alongside the other Heisei Kamen Riders to oppose Tid's forces.

Kamen Sentai Gorider Returning from Kamen Rider × Super Sentai: Ultra Super Hero Taisen and their self-titled web-exclusive sequel series, is a Kamen Rider/Super Sentai hybrid team composed of , , , and .

In Kamen Rider Zi-O the Movie: Over Quartzer, the Goriders appear from a bystander's tablet as part of the Heisei Riders' reinforcements against the Quartzers' Kasshine army.

Kamen Rider Fuma , a.k.a. was an executive of the foreign video game company who sought to turn the world into a virtual reality for his daughter before he was foiled by Ex-Aid and his allies.

In an alternate reality, Nagumo succeeded in his plans before he is summoned to Another World by Swartz to help him achieve his goals, only to be destroyed by Kamen Rider Woz.

Instead of being reprised by , he appears in a non-speaking role.

Gamedeus is the final boss Bugster created by Kuroto for Kamen Rider Chronicle.

An alternate reality version of Gamedeus was brought to Sougo's world following the Ex-Aid Ride Watch's destruction. Assisting Swartz in destroying the Kamen Rider multiverse, Gamedeus defeated Grand Zi-O until he was killed by Ohma Zi-O.

Instead of being reprised by , he appears in a non-speaking role.

Kamen Rider Fourze Kamen Rider Fourze , a.k.a. , is an alumnus and teacher of Amanogawa High School.

Despite having given up the Fourze Driver during the events of the crossover film Kamen Rider × Kamen Rider Wizard & Fourze: Movie War Ultimatum, his history as Fourze is erased by Another Fourze's creation. At the height of the Another Rider's killing spree, Gentaro goes off to investigate.

Year 2011: Kisaragi's fight with the Scorpion Zodiarts is interrupted by Another Fourze's creation, causing both the Rider's power and the Horoscope to vanish. At some later point in time, Sougo gives Kisaragi a blank Ride Watch to connect with in the future, which the latter entrusted to Ohsugi.

Instead of being reprised by , Gentaro Kisaragi is portrayed by an unidentified stand-in.

Chuta Ohsugi Returning from Kamen Rider Fourze, is a geography teacher at Amanogawa High School who serves as an academic advisor to the Kamen Rider Club. Kisaragi entrusts him with the Fourze Ride Watch so he can give it to Sougo and Geiz on Kisaragi's behalf.

reprises his role as Chuta Ohsugi.

Daita Kondo and Chikao Nezu Returning from the film Kamen Rider × Kamen Rider Wizard & Fourze: Movie War Ultimatum, and are members of the Monster League, a team of psychic students who were manipulated by Kageto Banba, until they are reformed into the Youth League.

As a result of Another Fourze's creation, Daita and Chikao became members of the Kamen Rider Club, assisting Sougo and his friends when Another Fourze attacks Amanogawa High School.

and reprise their roles as Daita Kondo and Chikao Nezu respectively.

Stardust Ninja Dustards are ninja-themed foot soldiers of the Horoscopes.

In a possible future in 2022, the Dustards joined Yaminin's Niji no Hebi and fight Kamen Rider Shinobi.

Sagittarius Zodiarts