Kazumi Sawatari

Kazumi Sawatari is the Kamen Rider of Hokuto. He later allies with Sento Kiryu and co. after his nation is invaded by Seito. He is a protagonist in Kamen Rider Build.

Past
Kazumi was originally the owner of a family farm in Hokuto, where he employed Akaba, Aoba and Kiba as his workers. However, after the Sky Wall Disaster occurred, virtually all of the land in the region was rendered infertile. Rather than lay off his workers, Kazumi used his savings to help support them and their families.

After his savings were depleted, Kazumi offered himself up to be experimented on as a test subject by Faust so he could keep supporting his employees. He told Blood Stalk to tell his workers that he had lost his memories as a side effect of the experiment.

In preparation for Hokuto's invasion of Touto for the, Kazumi was placed in charge of a strike team and tasked with acquiring Touto's Fullbottles and Pandora Box panels. Soichi Isurugi provided him with a Sclash Driver that would allow him to transform into Kamen Rider Grease. The rest of Sawatari's team was comprised of his three workers who, feeling indebted to their boss for his sacrifice, had allowed themselves to be turned into Hard Smash.

Hokuto-Touto War
After Prime Minister Yoshiko Tajimi declared war on Touto, Kamen Rider Grease spearheaded Hokuto's advance into the neighboring nation, penetrating the Skywall to get through.

He was encountered by Ryuga Banjou as he was searching for the Hokuto Three Crows. When a Strong Smash Hazard suddenly appeared and began attacking bystanders,, Kazumi destroyed the Smash in one punch using his hidden Helicopter Fullbottle before Ryuga had a chance to use the Build Driver. He later showed up to challenge Sento and Ryuga after they defeated the Hokuto Three Crows.

During a fight with Kamen Riders Build and Cross-Z, Kazumi lost Aoba when Build went on a brutal rampage induced by Hazard Trigger's affects and killed him. After canceling Sento's form, Kazumi went over to Aoba who handed his name tag over to Kazumi before dying and disintegrating into blue smoke.

When Seito took advantage of the displacement of Hokuto's troops to launch an invasion of the country, Kazumi and the remaining Crows entered into a fight with the Washio brothers. During the fight, Kiba sacrificed himself to block a finisher from Remocon Bro's. As he laying dying, Kazumi called Kiba by his real name, revealing that he hadn't actually lost his memories. Kiba then handed his dog tag over to Kazumi before disintegrating into yellow smoke.

Kazumi went on to witness Akaba being killed by Kamen Rider Rogue, with Akaba's final words being to thank his boss for everything. Kazumi ran up to Akaba, calling him by his real name as he disintegrated into red smoke and left his dog tags behind.

Kazumi would later make a grave for the Three Crows at Sky Road. He continued to fight against Seito to ensure the well-being of the Crows' families.