Mariko Natsuki appears in the anime Witchblade as a supporting character. She is the owner of the Natsuki Building and the proprietress of the Marry's Gallery Dining Bar, a venue that also serves as a local gathering spot. Mariko serves as the landlady of the apartment building where the protagonist Masane Amaha and her daughter Rihoko live, providing them with a place to stay during their difficult circumstances.

In terms of personality, Mariko is initially presented as a brash and sharp-tongued woman who does not hesitate to speak her mind. Despite this outwardly tough exterior, she is genuinely kind-hearted and demonstrates a particular softness toward Rihoko. She often looks out for the young girl and offers practical support, showing a maternal warmth beneath her blunt demeanor.

Mariko's motivations are rooted in her role as a local business owner and landlord. She is not directly involved in the central conflicts surrounding the Witchblade, the NSWF, or the Dohji corporation, but she provides a stable, everyday presence for Masane and Rihoko. Her role in the story is primarily that of a supportive figure who offers a sense of normalcy and shelter in a world filled with supernatural battles and institutional threats. She does not possess any special combat abilities or supernatural powers; her significance lies in her grounding influence on the main characters.

Her key relationships are with Masane and especially Rihoko. She becomes a trusted adult in Rihoko's life, offering care and a safe space away from the chaos that follows Masane. Mariko's interactions with Masane are more businesslike at first, but she gradually shows concern for their well-being. There is no indication of major character development or an arc; she remains a consistent, reliable secondary figure throughout the series, defined by her practical kindness and no-nonsense attitude. No notable supernatural abilities are associated with her, as her strengths are her hospitality, pragmatism, and loyalty to those she cares about.