Kazumi Sawatari

Kazumi Sawatari (猿渡 一海) is a resident from Hokuto and the leader of the Hokuto Three Crows. In the earlier stages of the war, he was given a Sclash Driver and the Robot Sclashjelly to transform into Kamen Rider Grease (仮面ライダーグリス), as the Rider representative of Hokuto. Currently, he aids Touto and their Kamen Riders to fight against Seito and Evolto.

Background
According to Sawa's report, Kazumi was once the owner of his family's farm in Hokuto, with Akaba, Aoba and Kiba as his workers. However, as a result of the Sky Wall Disaster, virtually all the farmland in the region was rendered infertile. Rather than lay off his workers, Kazumi used his savings to help his employees and their families.

One day, Kazumi came across a man named Massugu Ubukata, who was attempting to take his grandmother to a hospital only for his path to be blocked by Hokuto soldiers. Giving the soldiers a beating, Kazumi enabled Massugu to proceed, and his grandmother made a full recovery.

When Kazumi's resources were depleted, he willingly enlisted himself to be a test subject for Faust to futher insure his workers' survival. Kazumi tells Stalk, who was leading the experiment, to lie to the workers by informing them that Kazumi lost his memories as a side effect of the experiment.

Shortly before Hokuto invaded Touto for the Pandora Box, Kazumi was chosen to lead a strike team in charge of retrieving Touto's Fullbottles and Pandora Box panels. He was given a Sclash Driver by Soichi Isurugi, allowing to become Kamen Rider Grease. Feeling indebted to their boss for his sacrifice, his three workers became Hard Smash, forming the rest of his strike team.

Indebted to Kazumi, Massugu Ubukata wished to join his side and as such, crafted dog tags for himself as well as Kazumi and the Hokuto Three Crows. However, Kazumi initially refused his gift and ask him to go back to Hokuto.

Reclaiming Hokuto's Fullbottles
"These are Hokuto's Fullbottles so I'm taking them back. But don't worry. I'll see you guys again soon... on the battlefield."

- Grease

Shortly before the outbreak of the War, Kamen Rider Grease took an expedition to Touto in order to reclaim the Phoenix and Robot Fullbottles for Hokuto. Coming across Touto's Kamen Riders Build and Cross-Z, whom were engaged in battle against a squad of Touto's Guardians, Grease swiftly destroyed the Guardians as he snatched the Fullbottles off Build's person before leaving as soon as he came. Though he did not get a clear look at his assailant, Build correctly deduced that he must be another Kamen Rider. Meanwhile, Grease watched the Riders of Touto from a distance, well aware that he would soon face them on the "battlefield".

Hokuto-Touto War
As Kamen Rider Grease, Kazumi led the Hokuto advance into Touto once war was declared by Prime Minister Yoshiko Tajimi. Penetrating the Skywall, Grease destroyed many Touto Guardians.

Ryuga Banjo encountered him as he searched for the Hokuto Three Crows. A Strong Smash Hazard appeared and began attacking bystanders, and as Ryuga put on the Build Driver, Kazumi destroyed the Smash in one punch using his hidden Helicopter Fullbottle before leaving. Later, after Ryuga and Sento had defeated the Hokuto Three Crows in Ryuga's first fight as Cross-Z Charge, Kazumi showed up to challenge them with his own Sclash Driver.

One fight with Cross-Z Charge was interrrupted by the Three Crows. Stating that they broke the rules, Kazumi relinquished the Kuma and Televi Fullbottles to Ryuga. He later caught up with Massugu Ubukata when he was defeated by Sento Kiryu, having exposed himself to Nebula Gas and becoming the Ice Smash. Engaging Build, Grease found himself bewildered by Sento's new KumaTelevi Best Match. Ultimately, however, Sento learnt the story of Massugu and Kazumi through Televi-san, and chose to return the Kuma and Televi Fullbottles to Kazumi. Left with Massugu, Kazumi realized that he was still holding on to the dog tags he had made for him and his comrades and finally accepted them, claiming that the jingling sound Massugu made when he walked irritated him.

Hokuto's Defeat
Hokuto and Touto decided to end the war by having a duel between their respective Kamen Riders. It looked like Hokuto would win because Kamen Rider Build was afraid of using the Hazard Trigger. Ultimately, Build used the unstable Hazard form to win the duel and the war. Little was accomplished, however, as both war-weary countries faced a common enemy in the Seito nation.

Seito's Uprising
At the end of the Hokuto/Touto war, it became clear that the two nations would have to team up to defeat the Seito nation, who began an aggressive campaign to conquer all of Japan. Soon after, one of the Hokuto Three Crows decided to defend his people from Seito's wrath, and was soon captured by the Washio Brothers, Kazumi had no other choice but to escape back to Hokuto with Akaba, only to be shot down by Fu Washio. Before sacrificing himself, Kiba gave his dog tag to Kazumi. The Kamen Rider then watched helplessly as Kiba died, rationalizing it as just a common occurrence of war.

Seito-Touto War
In the final stage of the Seito-Touto war, an arrangement was reached by both governments. Like before, the two nations would pit their Kamen Riders against each other. Build was hesitant to use his full power, as the Nabeshima Family was held hostage. Once Kazumi got the Nabeshima Family out of danger, he watched as Kamen Rider Build use the full power of the Full Full RabbitTank Fullbottle to defeat Rogue and end the war with Seito.

Personality
Kazumi's demeanor alternates between calm and composed to ruthless and hysterical, depending on whether he's fighting or not. Presumably, due to his usage of the Sclash Driver, Kazumi is obsessed with battle and finding a worthy opponent. He is not afraid to use lethal methods, going as far as attempting to deliver a Rider Kick to an untransformed Banjo.

However, Kazumi operates by a certain code: he insists on not targeting civilians as long as they stay out of the way, and decided against taking Build's FullBottles due to him butting in the battle, much to the trio and the Hokuto Prime Minister's dismay. He is also repulsed by Prime Minister Tajimi's plan to send unnecessary reinforcements to invade Touto.

He also secretly cares about his underlings, as he is against the Hokuto Prime Minister and Stalk's idea of giving the Three Crows more power by strengthening them with the Hazard Trigger, knowing that they will die after they are defeated. After the Three Crows become Hazard Smashes, Kazumi was visibly frustrated. This is also shown as Utsumi blackmailed Kazumi to defect from Touto and bring Pandora Box to save his remaining co-workers. Kazumi initially fell to despair since he can't betray his comrades and become relieved after confirming his co-worker's safety first hand.

Having seen people die in front of him before, Kazumi recognizes the seriousness of war, viewing death to be a natural part of a war. Though he was deeply saddened by Aoba's death, he conceded that Aoba knew that his own life was going to be at stake and that he died because he was weaker, though that did not change the fact that he was someone Kazumi cared about. While Kazumi bears no ill will towards Sento, he still resolved to have a fair fight with the latter that would be held in the proxy war between Touto and Hokuto. The only exception to this is Gentoku, as Kazumi states himself that he'll never forgive Gentoku for killing Akaba.

Since Kazumi is a huge fan of Mii-tan, he quickly loses his will to fight and even allows his enemy to escape if Misora is the one who helped them. It's later obvious that he is in love with Mii-tan, but when Akaba asked him about his apparent crush and the possibility of her being Sento's girlfriend, Kazumi denied it by claiming that Mii-Tan is everyone's idol. Kazumi has also been shown to be restless when he is physically close to Misora, leading to him having inner monologues on how to approach her in a romantic way.

Powers and Abilities

 * Hazard Level 4 Physiology: Kazumi has undergone an experiment from Faust which injected him with a certain amount of Nebula Gas. However, instead of mutating into a Smash, the gas retained his body without side effects (though he did feign memory loss in an attempt to distance himself from the Three Crows). His natural Hazard Level is much higher than most, as his Hazard Level starts at Level 4 during his introduction, allowing him to utilize the Sclash Driver to transform into Kamen Rider Grease. In Episode 19, Blood Stalk read his level, and it has risen to 4.2.
 * Fullbottle Augmentation: By using a Fullbottle in his hand without transforming, Kazumi can gain abilities based on said Fullbottle's traits:
 * Helicopter: Allows Kazumi to perform fiery punches. First used to defeat a Strong Smash Hazard.

Devices

 * Sclash Driver - Transformation device.
 * Sclashjellies - Transformation trinkets.
 * Fullbottles - Trinkets for granting abilities with the Sclash Driver and transformation with the Build Driver.
 * Build Driver - Secondary transformation device.
 * Blizzard Knuckle - Adapter for Build Driver and secondary personal weapon.

Weapons

 * Twin Breaker - Grease's personal weapon
 * Nebulasteam Gun - Rogue's sidearm weapon that Grease borrowed to help his comrades escape from Evolto and Mad Rogue.

Team Build

 * Sento Kiryu: He and Sento were enemies during the Touto-Hokuto war. Feeling guilty for killing Aoba while under the influence of the Hazard Trigger, Sento begged Kazumi to kill him as a means of suicide. But Kazumi rather face him in the proxy battle, regardless of the sin Sento caused unknowingly. After the Hokuto proxy battle, with Seito waging war, Kazumi offered himself to join Team Build against Seito.
 * Ryuga Banjou: He and Ryuga were enemies during the Touto-Hokuto war. However, after they became allies, Sawatari is the only rider to call Ryuga Banjo by his first name while everyone else calls him by his last name.
 * Misora Isurugi: Misora as Mii-tan was Kazumi's idol and crush. When he saw her, he almost recognized her, until Sento threw him off for mistaken identity in order to protect her from Hokuto. After the proxy battle, hearing her voice and catchphrase from the net, he soon recognized Misora as Mii-tan close up. Joining Team Build, Misora only calls Kazumi "Grease" and not his real name.
 * Sawa Takigawa
 * Gentoku Himuro: Gentoku and Kazumi were enemies during the Touto-Seito war. Kazumi never forgave Gentoku for what happened to Akaba during the Touto-Seito war. Knowing revenge won't bring him and his comrades back, he makes Gentoku fight him in order to work with him and Team Build.

Enemies

 * Evolto
 * Nariaki Utsumi

Portrayal
Kazumi Sawatari is portrayed by Kouhei Takeda (武田 航平), who is more previously well known for his portrayal of Otoya Kurenai in Kamen Rider Kiva. As Kamen Rider Grease, his suit actor is Satoshi Fujita (藤田 慧).

Etymology
Following Sento and Ryuga, one of the kanji used to spell his name also represents an animal, Sa (猿), which poetically means "monkey". It could be referring to grease monkey, an English slang term for mechanics.