Yū is a young male character with long black hair parted down the middle, featuring long bangs framing his face and a distinctive braided ponytail tied with a white ribbon. Standing 142 cm (4'8") tall and weighing 39 kg (86 lbs), he possesses light gray eyes in the anime and crossed plasters on his forehead. His typical outfit includes a black jacket adorned with light buttons and cross insignia on the collar, worn over a blue sleeveless shirt featuring three white horizontal stripes, paired with black trousers and shoes. He often carries a large rucksack. Personality-wise, Yū shows kindness, responsibility, and courage. He works voluntarily as Vulcan Joseph's apprentice in mechanics and workshop operations, proving determined by scavenging for materials when suppliers refuse. His bravery is clear when he defends Shinra Kusakabe against Special Fire Force Company 5. Yū's involvement starts during the VS. Special Fire Force Company 5 arc, where Shinra rescues him from an Infernal attack. Later, in the Vulcan's Workshop arc, he helps Shinra, Arthur Boyle, and Iris meet Vulcan despite initial hesitation. He actively supports Vulcan's stance against Haijima, revealing Vulcan's father and grandfather were turned into Infernals—an event he suspects involves Giovanni. When Giovanni attacks the workshop, Yū is strangled as leverage to force Vulcan to surrender the Key to Amaterasu. After Iris treats his injuries, he returns to work alongside Vulcan. In the Arthur's Adventure arc (Netherworld arc), Yū accompanies Arthur, Lisa Isaribi, and Vulcan into the Nether to find orichalcum for reconstructing Excalibur.