Ryoma is the eldest son of Sumeragi and Ikona and the eldest child of four in the Hoshidan royal family. When Sumeragi married his second wife Mikoto, Ryoma helped the nation to warm up to the new queen by establishing a strong relationship with his new step-mother. Ryoma also recognized Mikoto's birth child, Corrin, as his new sibling. However, Ryoma lost this sibling when they were kidnapped as an infant and raised in Nohr. Prologue Ryoma first appears in Chapter 4, where he, along with Corrin, Kaze and Rinkah, lead a rescue attempt to save Hinoka and Sakura when they are ambushed by a horde of Faceless. Later at the Hoshidan capital in Chapter 5, the Ganglari blade wielded by Corrin explodes, killing almost everyone in the surrounding vicinity including Mikoto. As Corrin, wracked by grief and horror, responds by transforming into a feral dragon, a hooded man reveals himself as the perpetrator of the horrific deed, accompanied by a small troop of invisible soldiers. Ryoma attacks the hooded man but is forced to retreat after he is quickly defeated by him. Following the battle, he is forced to watch Azura risk her life to revert the dragon-crazed Corrin back to their human form after he is prevented from intervening. With war inevitable between Hoshido and Nohr highlighted by the now dispelled barrier due to Mikoto's death, Ryoma leads the Hoshidan army to the Plains of Hoshido where the Nohrian army awaits. As Prince Xander beckons Corrin to return to Nohr for their conquest, Ryoma calls Corrin to stay with their family by birthright. Depending on the side Corrin chooses, Ryoma's involvement in the plot will be altered.