Maaya Katagiri is the younger sister of Makoto Katagiri (sometimes referred to as Manami Katagiri). Her brother left middle school to work in a factory, determined to support her after their family struggled due to their father's criminal past. His earnings enabled her education, though she later failed her high school entrance exams. Both then enrolled in the same correspondence high school, where Makoto sought to build a better future.

Maaya possesses a lighthearted, cheerful nature, contrasting sharply with her brother's serious and often agitated temperament, shaped by his inferiority complex and resentment towards those more fortunate. Despite their situation, she recognizes and worries about Makoto's behavioral patterns, especially his unwarranted aggression towards classmates like Rio Ouzawa. She acknowledges the flaws in his outlook and implicitly encourages his emotional maturity and capacity to connect with others. Her presence acts as a grounding force in Makoto's life, reflecting his motivations and responsibilities while subtly fostering his growth throughout their shared time in the correspondence school.