Mayuri Shiina, a central character in the anime Steins;Gate and its film Steins;Gate The Movie - Load Region of Déjà Vu, is a gentle and optimistic young woman who serves as the emotional heart of the Future Gadget Laboratory. She is Rintaro Okabe's childhood friend and, after a period of depression following her grandmother's death, was claimed by Okabe as his "hostage" a role that gave her a sense of purpose and belonging. In the movie, Mayuri is one of the lab members who initially loses all conscious memory of Okabe after his consciousness begins to fade from the Steins Gate worldline due to Reading Steiner overload. Despite this erasure, she retains a deep, unexplainable sense of loss, which manifests as a lingering unease. Her personality remains consistently warm, carefree, and conflict averse. She dislikes tension and tries to maintain a cheerful atmosphere, often using her signature greeting "Tuturu" to lighten the mood. She is highly perceptive of others emotions, especially Okabe's hidden distress, and instinctively tries to comfort those around her.

Mayuri's primary motivation is to keep her friends safe and happy. She does not seek to understand the complex science of time travel but values the stability of everyday life. In the film, she becomes a crucial source of emotional support for Kurisu Makise, who is desperately trying to save Okabe. Even without remembering Okabe, Mayuri's compassion and her ingrained habits such as always keeping Dr Pepper for someone she cannot name help guide Kurisu toward the truth. Her role in the story is that of a quiet anchor; her very existence in the lab reminds the group of what is worth preserving. She does not directly participate in time travel or scientific breakthroughs, but her subconscious connection to Okabe acts as a catalyst for Kurisu's determination to retrieve him.

Key relationships define her character. With Rintaro Okabe, she shares a deep, sisterly bond that transcends timelines. Okabe has always been her protector, and she in turn provides him with emotional grounding. In the movie, Okabe's disappearance leaves a void in her heart even though she cannot articulate why. With Kurisu Makise, Mayuri develops a supportive friendship; she instinctively trusts Kurisu and encourages her when Kurisu feels lost. With Itaru Hashida, she maintains a casual, playful rapport that helps keep the lab environment light.

Development in the movie is subtle but meaningful. Having endured multiple traumatic timelines in the series, Mayuri experiences a peaceful life on the Steins Gate worldline, yet she is not immune to the aftereffects of Okabe's struggle. Her ability to feel a phantom connection to something missing shows her growth from a passive recipient of protection into an active emotional force that helps restore the worldline. Her notable abilities are not supernatural or combative but relational: she has a remarkable talent for reading emotional states, diffusing conflict without confrontation, and inspiring loyalty through pure kindness. She represents the ordinary, precious human bonds that the story revolves around, and her unquestioning love for her friends becomes one of the quiet forces that helps pull Okabe back from the edge of nonexistence.