Tomo, also known as the Angel (Tenshi), is Kei's younger brother. He lives with his father and older brother in Kawasaki, Kanagawa, near Tokyo. While their father outwardly presents them as a happy family, both brothers endure his emotional and physical abuse. Kei frequently shields Tomo from physical harm, intervening during beatings and reassuring him the situation is not his fault. Despite this protection, the abuse severely impacts Tomo, often leaving him in a dissociative state. He exhibits extreme fear of getting into trouble, reacting to even the suggestion by wanting to flee.

Within the virtual world "U," Tomo's avatar manifests as a small, angel-like clionidae: semi-transparent white with red dot eyes, wings, and a golden crown hovering above its head. A red heart-shaped orb at its core glows brightly during intense emotional experiences like fear or pain, reflecting his gentle, fragile nature in contrast to his brother's Dragon avatar.

Tomo becomes one of Belle's earliest supporters after her debut. Expressing admiration, he calls the Dragon his hero during an interview. He later guides Belle to the Dragon's castle, where he tends a garden of "secret roses" symbolizing rediscovered love, serving as a tribute to his mother who wore roses on her dress. When the Dragon shouts at Belle to leave, Tomo's avatar flees in fear but is comforted by the Dragon's reassurance.

During the Dragon's confrontation with the vigilante group Justices, Tomo's avatar appears weakened and faded. After the castle's destruction, he pleads for help for the Dragon in another interview but faces bullying from adults. In the real world, Suzu and Hiroka discover Tomo humming a song exclusive to the Dragon, though they initially don't suspect his connection. His father interrupts, accusing him of disobedience and attempting to strike him, but Kei intervenes.

After Belle publicly reveals her identity to gain Kei's trust, Tomo believes her sincerity and persuades Kei to contact her. Their father discovers the online exposure of his abuse and disconnects their livestream before they can share their address. Suzu locates them with friends' help. When their father confronts them, Suzu protects the brothers. Tomo later tells Belle she is as beautiful as her avatar. The aftermath remains undepicted, suggesting possible removal from their father's custody or relocation for Tomo and Kei.