|This article is about a/an temporary villain in Kamen Rider Build.|
- "Hokuto's rampaging tractor, Massugu Ubukata!"
- ―Massugu's roll call[src]
While tending to her farm in Hokuto, Massugu's grandmother suffered a heart attack, and so he attempted to take her to a hospital only for his path to be blocked by Hokuto soldiers. Seeing their plight, Kazumi Sawatari beat up the soldiers and allowed them to proceed. Thanks to his help, Kimiyo was treated in time and made a full recovery.
Massugu became indebted to Kazumi and, knowing that he was to be sent Touto alongside the Hokuto Sanbagarasu Akaba, Aoba, and Kiba, wished to join them in their crusade. To that end, he crafted a set of dog tags for the five of them as lucky charms. However, he was declined by Kazumi.
Despite being rejected, Massugu followed Kazumi to Touto where he found that Kazumi, now Kamen Rider Grease, relinquished his Kuma and Televi Fullbottles to Kamen Rider Cross-Z Charge. Following the Touto Rider to nascita, Massugu became the first customer of the neglected coffee shop ever encountered by Ryuga, whom provided him with a canned coffee. Eventually, Massugu found Sento Kiryu with the Fullbottles he sought and, seizing this opportunity, held Misora Isurugi hostage while using a Smash Bottle to expose himself to Nebula Gas, transforming into an Ice Smash. Engaging Kamen Rider Build's NinninComic Form, the Ice Smash's cryokinesis power proved superior to the Ice Smash Sento was familiar with, to the point of beating Build, who was forced to resort to the new KumaTelevi Best Match. Using Kuma Halfbody, Build discovered that he could weaken the ice by introducing an impurity and used honey from the Kuma Halfbody to weaken the Smash before defeating it with KumaTelevi's Vortex Finish.
At this point, Grease arrived, furious that Massugu had endangered himself, but he too was eluded by KumaTelevi. Massugu, however, persisted even after being forced out of his transformation. Through his new advisor Televi-san, Sento learnt Massugu's story and, understanding why he was indebted to Kazumi, conceded the Fullbottles to Massugu, whom he suggested would do better to return to Hokuto and continue supporting his grandmother before taking his leave. Massugu returned the Fullbottles to Kazumi, who told Massugu to give him his dog tags as the jingling they made when he walked annoyed him. Before taking his leave, Kazumi acknowledged that he had received Massugu's feelings and gave his regards to his grandmother.
Later, Massugu along with Kazumi's workers was held captive by Nariaki Utsumi, but was freed by Rogue when he chose to betray Namba. Later, they had a tearful reunion with their boss, and Massugu tells Kazumi that a purple Kamen Rider was the one who saved them last night.
Behind the Scenes
Massugu Ubukata was portrayed by Yuji Takao (髙尾 勇次 Takao Yuji).
- His version of Ice Smash also comes with a handheld freeze rifle, which he threw aside after briefly using it.