Rosyuo is the leader of the Overlord Inves and a major antagonist in Kamen Rider Gaim. He is a White Overlord Inves who is responsible for countless murders of the old civilization trapped in the Helheim Forest, and has targeted Japan next. He is also the previous individual chosen by the Helheim Forest, and holds the Forbidden Fruit of his realm.
His motive for everything is apparently caused by the results of his actions of making a "survival of the fittest" state into a reality, which destroyed his civilization, and making him outlive his wife, the "Over Lord Queen", whom he seeks to revive.
He is unaware of Redyue's plans to steal Forbidden Fruit he has guarded behind his back.
Rosyuo ordered Demushu to stop attacking humans and retreated. However, Deemushu kept disobeying it. Having no other choice, Rosyuo telepathically called him to cause pain to Demushu, making the Red Overlord Inves retreat. He later punished Demushu for disobeying his orders.
Rosyuo saved Takatora as he informed him about his origins. Rosyuo revealed the Helheim Forest was a civilization called "Femushinmu". He also tells that their civilization happily accepted Helheim and he was chosen by the Helheim to become the king. However, everything didn't turn out as he expected, as he had set the world into a Social Darwinist state. As shown, Demushu and Redyue killed their own people, showing the surviving strong had turned on each other. Rosyuo felt really guilty of what happened to his civilization and knows that the humans also will make the same mistake like him. Because of that, he won't give the forbidden fruit to anyone.
While informing Takatora about the Helheim's origins, including about his deceased wife, DJ Sagara appeared in front of Rosyuo to inform him that Demushu has recklessly struck Zawame City. Sagara also told Rosyuo that he has been cheating for having two forbidden fruit and suggested to give one of the forbidden fruit to the humans. Rosyuo then relinquished the forbidden fruit he guarded from his hand and turned it into the Kiwami Lockseed, giving it to Sagara to give to the rightful person to be its guardian.
Spotting an uninvited guest, Sid, Rosyuo shows how willing he is to prevent humanity from succumbing to the same mistakes as his own civilization by killing Sid, deeming him unworthy to have the forbidden fruit due to his foolish intention to use the forbidden fruit for his own selfish purposes. Once the human governments launch missiles at Helheim in response to its encroachment, Rosyuo becomes convinced that humans are barbaric and allows Redyue to continue the invasion of the Earth, shocking Takatora a lot.
Redyue later displayed a laptop computer to Rosyuo, showing him how advanced humans are. Believing that he finally had an opportunity to revive his wife, Rosyuo had Redyue construct a machine to revive the dead and sent his personal guard Grinsha to lead an army of Inves to gather humans to power it. After Mai Takatsukasa was captured, Rosyuo was approached by the Over Lords' human collaborator, Mitsuzane Kureshima, who asked him to keep an eye on her. Rosyuo soon took a liking to Mai however and selected her to be the carrier for Helheim's other Forbidden Fruit.
Rosyuo is later confronted by Kouta Kazuraba and Kaito Kumon, who sought to defeat him to halt Helheim's advancement. Rosyuo almost effortlessly defeated both of them, but was at that point betrayed and shot in the back by Redyue, who sought to claim the Forbidden Fruit for herself. However, as Redyue grabbed the Forbidden Fruit it withered away in her hands, signifying that the time of the Over Lords had come to an end. Enraged that her efforts to gain the Forbidden Fruit were all for naught, Redyue flies into a rage and brutally impales Rosyuo to death before being herself killed by Kouta.
Following Rosyuo's demise, his body was visited by DJ Sagara and the spirit of the Over Lord Queen, who expressed her hopes that humanity would not go down the same path that the Femushinmu did before disappearing. Rosyuo's Joeshimu sword later mysteriously wound up next to his wife's grave.
Though not much is known, Rosyuo has shown the ability to telepathically talk to other Over Lords and even cause them pain via telepathic feedback. As of right now, it is shown that Rosyuo possess a power that is beyond anything. With the myraid of powers such as telekinesis, Rosyuo is practically the god of his realm, able to fling targets far away, move rock formations such as mountains, and disintegrate any kind equipment, such as the Genesis Driver, through brute force alone.
- The origin of his name Rosyuo (ロシュオ?) might be coming from "Hakua" (はくあ?), means "Chalk" in Japanese.
- Rosyuo and the other Overlords seemingly has its own language. This is similar to the Gurongi Language from Kamen Rider Kuuga, the Undead from Blade and Fangire from Kiva, in which an enemy faction has its own language that the Japanese do not understand. As with the Gurongi, Japanese subtitles aren't provided for Rosyuo's speech, it is unknown if they will be provided in a later release such as a TV rerun or DVD release