Nao is the primary focus of the series. She breaks the typical "passive" mold often found in this genre. She is proactive, perverted, and deeply in love with her brother. Her character design—specifically her petite stature contrasted with the title's thematic focus on her brother's "size"—plays into the visual contrast that drives the series' appeal.
The story centers around the protagonist, a high school student who is struggling to navigate his daily life. However, his life takes a dramatic turn with the arrival of his little sister, who is just too adorable and talented for her own good. Despite her young age, she is ridiculously intelligent, athletic, and beautiful, making her an instant sensation wherever she goes. The series follows the hilarious and heartwarming interactions between the two siblings as they navigate their daily lives and the challenges that come with having a super-talented little sister. uchi no otouto maji de dekain dakedo mi ni konai best