根暗インキャ系オタクのすみれは、母親の再婚で義理の弟が出来て一緒に暮らすことに。初めて出来た義弟を溺愛し可愛くて仕方ないすみれ。義弟への想いがおさえきれない陰キャオタクのすみれは、独特のキモい喋り方で淫語をささやきながら義弟のことをねちっこく溺愛していく。断りきれない義弟への愛は暴走してどんどんエスカレートしていく！

Sumire, a gloomy, introverted otaku, gains a stepbrother when her mother remarries and they start living together. Sumire dotes on her first stepbrother and finds him irresistibly cute. Unable to contain her feelings for her stepbrother, the introverted otaku Sumire dotes on him obsessively, whispering lewd words in her unique, creepy way of speaking. Her uncontrollable love for her stepbrother spirals out of control and escalates more and more!