Dia holds the position of Chief Secretary for the Numazu Administrative Bureau, overseeing the town's bureaucratic functions and ensuring regulatory compliance. Her role requires strict adherence to rules and procedures, prioritizing orderly documentation and addressing any non-compliance. This perfectionist nature fuels her intolerance for unfiled paperwork or violations, reflecting a deep commitment to structured governance.

She is Ruby's sister. Ruby, a fairy descendant assisting Dia with administrative duties, strives to conceal her supernatural identity and maintain distance from humans. Despite her efforts, their sisterhood and Ruby's true nature remain an open secret within the community. Dia exhibits protective instincts, supporting Ruby's navigation of human interactions, including Ruby's voluntary ability to shapeshift into human form. They collaborate practically, with Ruby functioning as an equippable ally who integrates into Dia's specialized motorbike, enhancing its capabilities for transportation and town patrols.

As a public official, Dia demonstrates awareness of broader community dynamics, acknowledging Mari's contributions to town safety. She formally documents instances where Mari's interventions prevented accidents, such as identifying structural weaknesses in infrastructure, highlighting Dia's attention to both formal governance and Numazu's informal protective networks.

Dia utilizes specialized equipment for operational duties, notably the Scarlet Delta bodysuit-motorbike combo integrated with combat and mobility features. This equipment enables her to address emergent threats, including disturbances caused by corrupted gemstones that corrupt wildlife and environment. Her actions in these situations often involve coordinating with other residents to mitigate risks to the town.