"Sister-ism" is a manga series that explores the dynamics of sibling relationships through the lens of comedy and slice-of-life storytelling. The narrative centers around a group of sisters, each with distinct personalities and quirks, navigating their daily lives together. The eldest sister, often portrayed as responsible and level-headed, frequently finds herself mediating conflicts between her younger siblings. The middle sister is characterized by her energetic and mischievous nature, often causing playful chaos within the household. The youngest sister, typically depicted as innocent and curious, adds a layer of charm and naivety to the group dynamic.

The story unfolds through a series of episodic vignettes, highlighting the sisters' interactions at home, school, and in various social settings. Themes of familial bonds, personal growth, and the challenges of adolescence are woven into the narrative. The sisters' relationships are tested and strengthened through shared experiences, such as school projects, family outings, and personal milestones. Humor arises from their contrasting personalities and the relatable, everyday situations they encounter.

Supporting characters, including friends, classmates, and occasional parental figures, contribute to the richness of the story by providing additional perspectives and interactions. The manga balances lighthearted moments with occasional heartfelt scenes, emphasizing the importance of communication and understanding within a family. The art style complements the tone of the series, with expressive character designs and detailed backgrounds that enhance the storytelling. Overall, "Sister-ism" offers a charming and engaging portrayal of sisterhood, capturing the joys and challenges of growing up together.