Risa Koizumi

The protagonist of this work. Her height was 167 cm in the second year of junior high, 170 cm in the first year of high school, and 172 cm from the second year of high school (based on the height of Ninety-Nine's Hiroyuki Yabe). Her weight is 50 kg. Her birthday is August 3rd. Her blood type is O. Her family includes her parents and her younger brother Takahito, and although not living together, she has a grandfather. Her surname is derived from Junichiro Koizumi, who was the Prime Minister at the time the series began.

Ōtani usually calls her "Koizumi," but due to her tall stature, he occasionally calls her "Kyoonna" (a short form of "giant woman," referred to as "Dekaonna" in the anime) or "Giant Goddess," and she jokes about herself saying, "It's Koizumi, not Ōizumi." She's not good at studies or sports, but her interactions with Ōtani are top-notch, resembling a comedy duo, where she mainly plays the funny part. She was forced by her homeroom teacher Nakano to serve as the class representative for three years. Initially, she liked Suzuki, but after he started dating Chiharu, she gave up on him and later fell for Ōtani, though she couldn't be honest about her feelings until influenced by Seiko. Ōtani and she eventually became a famously recognized couple by their class and parents after various incidents. She has a simple, always bright, and positive personality that recovers quickly when flattered. Although not usually mentioned due to her goofy nature and the impression of being an "All Giant," she is actually quite beautiful. She was even said to look picturesque when standing next to Haruka. Since her second year of junior high, she has been a big fan of Umibōzu and is recognized as quite a gamer by herself and others. After graduating high school, her parents suggested she go to junior college, but she decided to go to a vocational school because she "didn't want to study for entrance exams," and at the suggestion of her best friend Nobuko, she decided to pursue a career as a stylist. Her favorite colors are red and yellow. Her favorite clothes are comfortable and cheap ones. Her favorite oden ingredient is egg. Her ideal type is "someone taller than herself and prince-like," and Mighty, mentioned later, is exactly her type. Therefore, at the beginning of her third year of high school, she formed the "Mighty Club" partly to spite Ōtani for being oblivious to her feelings. She became the first president but quit after Ōtani told her it was "creepy and to stop it."

In fact, she and Ōtani had accidentally met at an Umibōzu concert during the spring break after graduating from junior high, but it took three years for her to realize this, during the spring break after graduating from high school.