Duke Gateau (ガトー公 ) is an unused character in Ys V: Lost Kefin, Kingdom of Sand. He isn't mentioned in Ys V's original concept nor does he appear in any game.
He does however appear in Ys V: The Lost City of Sand (イースV―さまよえる砂の都), a non canon novel that borrows elements from Ys V's original concept and the game's story, resulting in a completely different tale.
Ys V Novel[]
In the novel, he is portrayed as the political rival and cousin of King Kefin, as well as the ancestor of Rizze. Duke Gateau opposes King Kefin's isolationist policies and advocates for aggressive territorial expansion through alchemy. Similar to the original concept, Kefin is depicted levitating above the ground, hidden from view. Jabir, who supports Kefin's isolationism, banishes both Gateau and Orwell—powerful alchemists—to the surface as the city begins its ascent into the heavens, viewing them as liabilities due to their opposition to the King.
Shortly after Kefin's ascension, the city starts to absorb the earth's energy, resulting in the surrounding land turning into a desert. Alarmed by this development, Orwell attempts to bind the floating kingdom to a limited area to mitigate its impact on the land, employing a "Sealing Circle" that requires crystals.
In the game, it is Jabir who sends soldiers after Foresta and the Lumen Crystal, but in the novel, this role is taken on by Gateau.
With the introduction of Duke Gateau, Rizze's character diverges significantly from the original proposal, leading Zwett to assume the original role of Rizze as Dorman's butler.