Kodama Kohinata, the younger sister of Hikari Kohinata, begins her journey in junior high before advancing to the same high school as her sibling. She possesses pale skin, chin-length blonde hair with bangs above the eyebrows, and green eyes. Kotori Misaki stands as her friend from school days. Kodama exhibits a contemplative nature, pondering future activities such as high school extracurricular choices during a New Year's Eve gathering. Her grandmother Kino responds with youthful diving tales, emphasizing perseverance through setbacks.

Kodama commits to diligent study alongside Kotori, securing admission to Yumegaoka High School. There, she joins the diving club alongside Hikari, Futaba Ooki, and others. At Mount Omuro's festival, she engages with Futaba and Kokoro Misaki, though she remains uninvolved when Kokoro aids Hikari and Futaba in an incident. Her development peaks during a club dive to a site her grandmother discovered years prior, marking her formal entry into the diving community. The surname "Kohinata," translating to "small sunny place" or "basking in sunlight," echoes themes of growth and warmth.