Rikka Hishikawa, a brilliant second-year student at Oogai First Middle School, fights as Cure Diamond in the DokiDoki! Pretty Cure team, embodying wisdom and wielding ice-based powers. Her dark blue eyes contrast sleek chest-length hair, often adorned with a delicate braid and ribbon, while her civilian outfits pair a white blouse with a blue bowtie and a light blue pleated dress. Transformed into Cure Diamond, her knee-length light indigo hair cascades into a ponytail, accented by blue diamond earrings, a flowing light blue dress with wing-like sleeves, and crisp white boots.

Academically exceptional, Rikka consistently ranks nationally but faces fluctuations when hobbies divert her focus. Her composed demeanor masks blunt honesty, serving as a steadfast counterbalance to her impulsive childhood friend Mana. Their enduring bond features mutual protectiveness, with Rikka persistently—if unsuccessfully—trying to temper Mana’s zeal. She navigates team dynamics skillfully, initially clashing with Makoto over rivalry before forging trust through candid dialogue alongside Alice.

Initially hesitant to accept her role as Cure Diamond, Rikka embraces it after obtaining a Lovead and witnessing Mana’s vulnerability in battle. Her transformation, activated by the Lovely Commune and the chant "Pretty Cure, Love Link!", unleashes icy assaults like Twinkle Diamond and Diamond Shower. A defining moment arises when she shields former adversary Ira, defying allies to act on empathy and moral conviction. This bold choice triggers a power awakening rooted in self-trust.

In *Eiga Precure All Stars New Stage 3: Eien no Tomodachi*, Rikka collaborates with fellow Pretty Cure warriors to combat a dream-consuming fairy imprisoning children in comas. Though her individual actions remain unspecified, her studious nature and compassion align with the united front to reclaim the dream realm. Her narrative intertwines scholarly ambition with guardian duties, reflecting a balance between personal growth and selfless heroism.