16 years old. Student of Aoba High School. Hotaru is a genius of robotics and is the creator of the robot who attended the scholastic competition of her school and came in third place. After the first Derinjer attack, her robot was developed and transformed into Robot Rob in the Robot Center of her father, Professor Mizuki. Hotaru is also the captain of the Aoba High School Tennis Team, for which she is always surrounded by admirers willing to conquer her despite having a weakness for Daisaku.