"My Stepsister Tries to Hypnotize Me" centers on the life of a high school student whose family dynamic shifts when his father remarries, introducing a new stepsister into his life. The stepsister, a seemingly sweet and caring individual, harbors a hidden fascination with hypnosis. She begins to experiment with her newfound interest, using her stepbrother as her primary subject. The story explores the gradual escalation of her attempts to hypnotize him, blending moments of humor, tension, and psychological intrigue.

The protagonist, initially skeptical of hypnosis, finds himself increasingly drawn into his stepsister's experiments. Her methods range from traditional techniques to more unconventional approaches, often leading to awkward or comedic situations. As the story progresses, the stepsister's motivations become more complex, revealing layers of her personality and the underlying reasons for her fixation on hypnosis. The dynamic between the two characters evolves, oscillating between playful sibling rivalry and moments of genuine emotional connection.

Supporting characters, including classmates and family members, occasionally become involved in the stepsister's schemes, adding variety to the narrative. The manga balances lighthearted comedic elements with subtle psychological undertones, creating a unique tone that keeps the story engaging. Themes of trust, boundaries, and the complexities of blended family relationships are woven throughout the plot, providing depth to the otherwise whimsical premise. The series maintains a focus on character development, particularly in exploring the evolving relationship between the protagonist and his stepsister as they navigate their unusual circumstances.