Ruri Tanigawa is a high school student fascinated by jewelry and minerals. She possesses long orange hair, frequently noted as yellow or blonde, and emerald green eyes. Her typical outfit is a white short-sleeve hoodie.

Limited financial resources initially prevent her from buying desired jewelry, such as a quartz point necklace. This situation motivates her to search for crystals independently in the mountains. During this search, she encounters Nagi Arato, a graduate student in mineralogy. Under Nagi's mentorship, Ruri actively engages in mineral collection, developing practical geology and mineralogy skills. She learns to use tools like rock hammers and gains knowledge in geological concepts including pegmatites, plate tectonics, and erosion processes.

Ruri's character evolves from an initial focus on jewelry's aesthetic and monetary value toward appreciating minerals for their scientific significance and the geological stories they tell. On a gold prospecting trip, her initial excitement over pyrite—mistaken for gold—shifts to understanding its scientific value in refining geological hypotheses. Later, upon discovering a substantial gold nugget formed over millions of years, she chooses to keep it for its historical and scientific importance rather than sell it. Her curiosity and expressiveness fuel her increasing involvement in fieldwork activities like splitting rocks, performing streak tests, panning for placer gold, and exploring geological formations such as riverbed potholes.

Her relationship with Nagi centers on mentorship, where Nagi's guidance helps her appreciate geology's interdisciplinary nature. This includes recognizing how unexpected mineralogical findings can challenge and expand scientific theories. Ruri's experiences foster a deep appreciation for hands-on scientific exploration, shifting her aspirations from owning jewelry to actively participating in earth sciences.