A high school student with a passion for jewelry and shiny accessories, Ruri Tanigawa finds herself unable to afford an exquisite crystal necklace she sees in a shop. Her mother mentions that her late grandfather was once a mineral collector, but that his entire collection has sadly been given away. Refusing to give up, Ruri decides to venture into the nearby mountains to search for and collect the raw crystals herself, hoping to recreate the piece of jewelry.

What she lacks in knowledge and equipment she makes up for with determination, but Ruri quickly finds herself lost and overwhelmed in the wilderness. It is during this first expedition that she encounters Nagi Arato, a composed and highly knowledgeable graduate student studying mineralogy. Nagi guides the inexperienced but enthusiastic Ruri to a stunning deposit of quartz crystals, explaining basic concepts like pegmatites and how erosion brings minerals to the surface. By the end of her trip, Ruri has not only collected her first beautiful crystal specimens but has also developed a newfound passion for the scientific aspects of mineralogy, begging her mother for her own geological hammer so she can continue her hunts.

The story follows Ruri as she is drawn deeper into the world of earth science, transitioning from a casual admirer of gemstones to a dedicated amateur mineralogist. Under Nagi’s patient mentorship, she learns to use professional tools like panning dishes, topographic maps, and ultraviolet lights. Her journey expands beyond solo adventures to include a group of friends and colleagues. They are joined by Yōko Imari, Nagi’s underclassman who excels at historical research but struggles with physical fieldwork, and Shōko Seto, Ruri’s best friend whose childhood fascination with rocks is rekindled by Ruri’s enthusiasm.

The narrative is driven by a series of mineral-hunting expeditions, each focused on a different treasure. Early arcs cover the search for common but beautiful minerals like garnet, pyrite, and fluorite. A significant arc involves gold panning in a historic mining district, where Ruri learns the frustration of finding worthless fool’s gold before successfully discovering real flecks and small nuggets in a riverbed after a heavy rain. Another key storyline takes the group to an abandoned mine, where they become trapped in a collapsed tunnel. They navigate the darkness using Nagi’s UV light, which spectacularly reveals fluorescent crystals of fluorite lining the walls like a hidden starry sky, leading to a formal scientific study led by the reluctant Yōko.

The setting ranges from riverbeds and high mountain peaks to dusty university labs and deep, perilous caves. A recurring theme is the contrast between the commercial value of finished jewelry and the intrinsic beauty and scientific worth of raw, unpolished stones. Ruri embodies this shift as her initial desire to own pretty baubles transforms into a deep appreciation for the geological history, chemical composition, and ethical collection of natural specimens. Eventually, Ruri even contributes to a scientific paper and participates in a meticulous sand survey to pinpoint the source of a sapphire deposit, proving that her journey is taking her far beyond a simple hobby.