Raiko, known by the epithet the Sage, is one of Yamato's Eight Pillar Generals in Utawarerumono: Mask of Truth and the elder brother of Mikazuchi, the Left General of the Imperial Guard. He is a tall, slender, handsome man who favors white and purple clothing, and his standing rests entirely on his intellect rather than his physical strength. He is regarded as Yamato's foremost strategist, a commander said to be able to reduce any impregnable fortress through sheer tactical brilliance alone, without ever needing to take the field in person.

In temperament, Raiko is cold, composed, and ruthlessly calculating. He consistently prioritizes results over morality and is willing to accept any sacrifice to achieve victory. He treats the soldiers under his command as instruments of his plans, and his methods include psychological manipulation as well as military strategy. When the spirit of his finest tactician fails him, he has the man brainwashed in order to retain his services, and he destroys the great Bridge of Inava not only for military expediency but also to make a point. Despite this coldness, he shows glimpses of genuine family feeling: he takes an interest in his brother's guests, speaks of their mother with warmth, and reminds Mikazuchi to visit her.

His motivation in Mask of Truth is rooted in his belief that Yamato needs strong, decisive leadership. After the death of the Emperor plunges the imperial capital into chaos, Raiko seizes the moment to maneuver for control of the nation. He installs a false princess and works to consolidate power, presenting his actions as being undertaken for the sake of the country. His ambition is not mere opportunism but a conviction that his own cold and calculating vision is what Yamato requires to endure its crisis.

Raiko serves as the principal antagonist for most of the story. While the true princess Anju and her allies flee to Ennakamuy, Raiko takes control of the imperial capital behind the false princess and directs the imperial court army against them. He wages war from a distance, preferring to orchestrate events through schemes, misinformation, and manipulation rather than confronting his enemies directly. His machinations force the protagonists into a desperate struggle across Yamato, and he remains the strategic brain behind every major threat they face until the Ennakamuy forces finally retake the capital and bring his rule to an end.

His key relationships reflect both his humanity and his ruthlessness. With Mikazuchi, he is affectionate yet controlling, holding his brother back from intervening in the turmoil and deploying him as the martial arm of his plans. Shichiriya, his calm and capable adjutant, faithfully executes his intricate orders with speed and precision and is one of the few people he trusts. He also makes use of the broken tactician he has brainwashed, turning a talented mind into a tool of his strategy. Against Oshutoru and the allies who rally around Anju, he is a patient and dangerous rival whose intellect shapes the entire conflict.

Raiko's notable ability is his strategic genius. He avoids direct combat and wins wars through indirect means, relying on preparation, deception, and the calculated use of his subordinates. Even when finally faced on the battlefield, he proves a formidable opponent, fighting as a powerful boss supported by Shichiriya, with techniques associated with the darkness element that make him dangerous even in direct confrontation. Over the course of the story he develops from an amused and sharp-witted observer into the story's central villain, and his carefully built plans ultimately crumble against the unity and determination of his opponents, ending with the loss of the power he had seized.