The Onii-chan wa Oshimai! Oyama Mahiro figure is created in a refined 1/8 scale that captures a lively, feminine presence while preserving the character's distinctive aura from the series. The sculpt emphasizes clean lines and soft curves, with carefully painted hair strands, delicate facial features, and subtle shading to convey Mahiro's expressive mood. The pose suggests movement and confidence, balanced by a stable base that hints at the everyday setting the show portrays. Materials give a smooth, slightly glossy finish that highlights the character's outfit and accessories, with attention to tiny details and high-quality craftsmanship.

Oyama Mahiro is the central figure in Onii-chan wa Oshimai!, a fantasy comedy in which a magical transformation changes the main character's life. The story follows Mahiro as they navigate school, friends, and family while adjusting to new circumstances brought on by the transformation. It balances humorous situations with moments of genuine emotion as Mahiro learns about identity, resilience, and how others react to their changed appearance. The narrative often explores themes of self-acceptance, family bonds, and the idea that character and heart matter more than outward form.