Natsumi Asaoka, nicknamed "Eru" or "L" for "Large" or "L Size," transfers into Sunshine High School. Standing 1.80 meters tall, she is significantly taller and more busty than average Japanese girls her age, which naturally draws attention. Despite this, she keeps a cheerful and agreeable disposition. Her personality blends intelligence and approachability with judicious decision-making and a streak of energetic stubbornness. She displays comfort with her body, having no objection to her boyfriend Shunsuke Aoba seeing her nude or touching her breasts. Kindness motivates many of her actions, such as helping Shunsuke overcome his discomfort around women to assist customers at his mother's fashion boutique.

She lives in the school dormitory. An early incident saw her punished—denied dinner—after Shunsuke was discovered in the girls' dormitory where she had brought him to treat a sprained foot. In response, Shunsuke secretly returned to give her red-bean paste bread.

Her relationship with Shunsuke began when he, also a new transfer student, encountered her at school. Though initially surprised by her size, he treated her normally rather than as an oddity, earning her deep appreciation and growing affection. Their dynamic features contrasts: her gentle, statuesque presence complements his short stature and gruff, tsundere tendencies. She consistently supports him, mediating his social interactions and standing by him during conflicts with figures like the stern teacher Michi Kaneko or dorm leader Monta Akai.

Her narrative focus centers on her school life, relationships, and integration into Sunshine High.