Akaba

"Boss... thank you... for everything," - Akaba's last words, before handing Kazumi Sawatari his dog tag.

Akaba  (赤羽 Akaba) is one of the minor antagonists in Kamen Rider Build. He was born as Masaru Ooyama (大山勝 Ōyama Masaru, but after being experimented on and joining Kazumi Sawatari, he was given the name Akaba, thinking that Kazumi would actually refer him as so. Later in the series, Akaba becomes part of Sento's team, after Kazumi lost the proxy battle. He uses the Castle Fullbottle to transform into Castle Hard Smash. Later on in the series, he gets upgraded into Castle Hazard Smash. He is portrayed by Eishin.

Graphite

"Cultivate," - Graphite's catchphrase before transforming into his Bugster form.

Graphite (グラファイト Gurafaito) is one of the main antagonists from the series Kamen Rider Ex-Aid. He is one of the Bugster executives, along with Parado, who inserted a Proto Drago Knight Hunter Z gashat into himself, to be a Bugster of it. His main goal is to simply eliminate the human race. He is the Bugster who infected Saki Momose long ago.

He uses the Gashacon Bugvisor to infect people, mostly at the first part of the series. He is one of the High-Tier of the Bugsters, with Parado and Lovellica. He is portrayed by Shouma Machii.