Hiroka Betsuyaku, known as Hiro or Hiro-chan, is Suzu Naito's closest friend and sole confidante. She alone knows Suzu's secret identity as the virtual singer Belle. Hiroka exhibits sharp wit and incisive communication skills honed through extensive online activity. She actively manages Belle's career within the virtual world "U," handling promotion and protecting Suzu's anonymity.

Hiroka's father, Mr. Betsuyaku, once questioned her laughter and subsequently restricted her access to a room in their house; her mother, Mrs. Betsuyaku, relayed this action to her. Despite claiming to have no secrets, Hiroka maintains a lock screen wallpaper featuring a photograph of their physics teacher, Mr. Terada. This concealed admiration suggests a potential crush, causing her embarrassment and remaining undisclosed to her parents.

In "U," Hiroka operates under the alias "eroh," an avatar designed by concept artist Ippatu. Her technical skills and strategic thinking prove vital for navigating the platform, especially during critical events involving the vigilante group Justices and the mysterious user Dragon. She collaborates closely with Suzu to investigate the Dragon, uncovering his link to abused teenager Kei and younger brother Tomo. When Kei distrusts Suzu's offer of help, Hiroka supports Suzu's decision to reveal her identity as Belle during a global "U" broadcast, a pivotal move to demonstrate genuine intent.

After the brothers' internet is disconnected by their abusive father, Hiroka helps analyze clues to locate them in Kawasaki, Kanagawa Prefecture. She provides unwavering support for Suzu's subsequent real-world journey to protect Kei and Tomo, reinforcing their friendship through practical aid and emotional solidarity. Hiroka's consistent presence underscores her role as a foundational pillar in Suzu's life, bridging their everyday experiences with extraordinary online events.