Nozomu Tanaka, universally nicknamed "Baka" for her exceptionally low intelligence and frequent foolish behavior acknowledged even by close friends, stands 158 cm tall and weighs 41 kg. She has brown hair cut to neck length, gray eyes, and blood type O. Baka exhibits extreme optimism and a perpetually carefree attitude, often smiling despite mockery over her lack of intelligence. While her academic scores are consistently low, ranging from 10 to 50 across subjects, she occasionally demonstrates unexpected problem-solving abilities, solving puzzles or offering solutions to friends' problems. Her defining catchphrase, "Hey, guys! Do you want to hear something amazing?", typically precedes nonsensical statements.

She maintains childhood friendships with Akane "Wota" Kikuchi and Shiori "Robo" Saginomiya dating back to elementary school. In junior high, she helped Utako "Hime" Nakamura overcome bullying by bestowing the confidence-boosting nickname "Hime" (Princess), which also inspired improvements to Hime's family's failing ramen shop. Baka attends a school with mediocre academic standards, entered after sleeping through the admission exams.

Her core traits remain consistent across adaptations. The anime expanded minor scenes like the "Nudist Family" discussion where friends solidified her nickname and added original content such as a pool episode and pig farm segment. The live-action adaptation introduced the "Robokko" subplot focused on Robo. No significant evolution or backstory expansion occurs in spin-offs or other media.