Hoshino wears a navy blue suit over a white dress shirt. He has a medium-length hair and can be seen wearing a black backpack whenever he is outside of the office.
Hoshino is a new lawyer who works at Ryuzo Genda's law office. He passes the bar examination with flying colors on his second attempt.
At the beginning of chapter 4, Saori Shirosaki accuses him of eating her special cake that she had left in the fridge at Genda law office. She decides to rope in Mafuyu Fujii and Takayuki Yagami as prosecutor and defence lawyer respectively for a makeshift "trial." After investigating the "crime scene," Yagami successfully manages to argue that in fact no-one had eaten the cake: it had gone off after the fridge had been deprived of power for a number of hours the previous night, and Ryuzo Genda had thrown the contents out as part of his first time on cleaning duty.
- Hoshino holds a third-degree black belt in karate. Despite this, he is never seen fighting.