Hikaru Sofue is an 11-year-old resident of Kamimai City who becomes the first person protagonist Yuta Akikawa meets upon his arrival in the technologically advanced city. Their initial connection forms when she helps him operate a soda machine. They soon become classmates.

Hikaru exhibits a lively and friendly personality coupled with above-average intelligence, reflected in her strong academic performance. She shares her protective grandfather Juzo Sofue's aptitude for computers and technology, readily demonstrating this skill by assisting Yuta with computer systems. She also possesses a distinct fondness for plants. Her family includes her grandfather, Juzo, an internet technology specialist who rejects the philosophies of the corporation Dream Future, and an older sister named Miharu Sofue.

As Yuta adapts to Kamimai City, Hikaru frequently guides him, explaining local customs and technology. Her role deepens when she gains the ability to access the Net World through her partnership with Ecolon, an ecology-focused web ghost linked to her favorite website. Without Ecolon, she cannot independently "net dive" unless accompanied by someone else with that capability.

Within the Net World, she collaborates with Yuta and his web ghost companions, Pit, Pot, and Pat (collectively PiPoPa), contributing to resolving technological disruptions and combating digital threats. She also assists friends in the physical world, such as helping classmate Karin Yukitani establish a website for her family's inn. Her relationship with Yuta includes a noted possibility of romantic feelings. Classmate Kazushige Enoshima develops a crush on her, leading to frustration when Yuta interacts closely with her or another classmate, Sayaka Erenkova.