Ren Aoi

Ren Aoi is a mysterious man, who transforms into Kamen Rider Fifteen Skeleton, created by the Badan Empire in order to defeat the Kamen Riders. He is the father of Jen Aoi]] and husband of Saki Aoi]

Past
Ren Aoi is a family man when his son was alive. After his son died in an accident while having to do with meeting his wife at a lighthouse, Ren falls into despair after losing his son. When his son is in fact alive, Ren joins the Underground Empire Badan, becoming their Kamen Rider to find his still alive son, but somehow got brainwashed into their pawn.

Present
Kamen Rider Fifteen first appears to fight the 5 mysterious warriors, but is interfered by the first three Kamen Riders. The three riders manage to drive off Fifteen, as he enters through a darker version of a Helheim Crack.

After finding his son at Zawame City, Ren appeared in his normal identity, battling Armor Warrior, Baron, Dragon Defender and Moon Blade Final, transforming into Fifteen Skeleton, able to defeat Moon Blade Final then later Dragon Defender, thanks to Heisei Rider Lockseed he use as Ringzard Arms. His battle with Armor Warrior is interrupted by three very first Kamen Riders, leading Armor Warrior to escape with Shu and Mai to safety. He found his son again in his home destroying the message that Shu made for his mother and tells him to come in order to use Shu's power for the Mega Reversal Machine. However, his son refused because Ren began to act strangely due to him being brainwashed, thus leading to Ren forcing his hand to take him away from Heisei Riders' protection. Upon his son finally caught nearby the lighthouse where his wife, Saki is, Fiftee Skeleton managed to take his son away from the Heisei Riders and meet his wife. He is defeated by Kamen Rider Armor Warrior 1 Arms after he was overpowered by his 1 Squash, destroying his Sengoku Driver and its Yomimaru, thus freeing him from Badan's grasp. After realizing for what he did when he was brainwashed by Badan, his son began fading away, but managed to take his son to the lighthouse to reunite with his wife, thanks to the Riders (mostly Showa Riders' Rider Syndrome teleportation) and seeing their son disappear to the top of sky as a light above them.

Arms
Like his fellow Lockseed-using Armored Riders, Kamen Rider Fifteen Skeleton's forms are called Modes while the armor is called Arms.

Ride Wear
The Ride Wear is Fifteen Skeleton's default form undersuit, which is briefly seen during Fifteen Skeleton's transformation sequence before the Armor Part attaches or when he changes Arms. However, this form is completely vulnerable to any incoming attacks when shot at directly in the suit rather than at the Arms that is descending down on the Rider.

The Ride Wear that Fifteen Skeleton's Sengoku Driver has is easily identifiable through its Rider Indicator faceplate. The Rider Indicator only identifies what Ride Wear a Sengoku Driver contains for simplicity and can be replaced with extensions such as the Genesis Core or Ultra Joint.

Notably, this is not a step in his transformation to his regular form.

Fifteen
Ability Perimeters: Fifteen Arms is Fifteen Skeleton's default skeleton-based form, which is accessed through the Fifteen Lockseed. Unlike other standard Lockseeds, this one has no accompanying phrase similar to most of the Energy Lockseeds, though it also lacks the call of "Fifteen Arms" by instead just having the music, Arms Weapon is the Yomimaru. Similar to how Legend Rider Armor Parts appear as the head of the represented Rider before transformation, the Fifteen Armor Part initally appears as a skull not unlike the original appearance of the Generalissimo of Badan.
 * Punching power: 15 t
 * Kicking power: 21.5 t
 * Maximum jump height: 51 m
 * Maximum running speed: 100 m per 5.1 sec.

Interestingly, when Fifteen transforms into this form, he bypasses the Ride Wear stage entirely as the armor and his suit form at once.

Rider
The Rider Arms are forms based on past Kamen Riders.

Chrono Warrior
Chrono Warrior is a Legend Rider Arms based on Kamen Rider Chrono Warrior's default form, which is accessed through the Heisei Rider Lockseed channeling the Chrono Warrior Lockseed, this form's Arms Weapon is the Ride Booker.

Similar to Chrono Warrior himself, this form allows Fifteen Skeleton to use the power of the first Nine Heisei Riders as seen when he activates his Sengoku Driver's (Echo Demon) Squash function, manifesting an Ongekibou Rekka to counter the one used by Chrono Warrior as Kamen Ride: Kamen Rider Echo Demon. Chrono Warrior Arms' ability to use the power of the previous Heisei Riders without changing Arms is not unlike Chrono Warrior's own Violent Emotion form or Armor Warrior's Extreme Arms

Another ability of Chrono Warrior Arms is allowing Fifteen Skeleton to channel the power of Chrono Warrior's Attack Ride cards, as seen when he activates a Chrono Warrior Squash attack while fighting Kamen Riders Chrono Warrior, Kamen Rider Double Detective, Quadronaut, and Ringzard. Charged into the Ride Booker, he unleashed a series of slashes against his opponents amplified by self-replication (Attack Ride: Illusion) and multiple slash (Attack Ride: Slash) abilities.

Quadronaut
Quadronaut Arms is a Legend Rider Arms based on amen Rider Quadronaut's Base States, which is accessed through the Heisei Rider Lockseed channeling the Quadronaut Lockseed, this form's Arms Weapon is a rotation between the Cosmic Module Barizun Sword (primary) and Elek Module Billy the Rod (Fourze Au Lait) instead of Rocket Module used by Kamen Rider Moon Blade.

Ringzard
Ringzard Arms is a Legend Rider Arms based on Kamen Rider Ringzard's Flame Style, which is accessed through the Heisei Rider Lockseed channeling the Wizard Lockseed, this form's Arms Weapon is the WizarSwordGun.