Kana Sôma is a woman from a branch family of the Sôma clan, making her an outsider not bound by the curse of the Chinese Zodiac. Before the main story begins, she is employed as an assistant to Hatori Sôma, the family's physician. She is a gentle, friendly, and caring person with a notably positive and cheerful attitude. Hatori himself observes that her personality is very similar to that of Tohru Honda, a later acquaintance. Kana is also described as having an unpretentious and outgoing nature. Her sensitivity and emotional depth, while often a source of warmth, also make her vulnerable in difficult situations.

The central motivation driving Kana’s actions is love and acceptance. She is particularly memorable for a question she asks Hatori about what snow becomes when it melts. When he logically answers "water," she gently corrects him, explaining that it turns into spring, a philosophy of hopeful transformation that defines her outlook. Upon discovering Hatori’s secret transformation as the Sea Horse of the zodiac, she does not recoil but fully accepts him, which deepens their relationship. Her hope is to build a life with him, and they eventually seek permission from Akito, the head of the family, to marry.

Her role in the story is largely tragic and serves as a pivotal part of Hatori Sôma’s backstory. Kana’s relationship with Hatori becomes a catalyst for illustrating the destructive power of the zodiac curse and Akito’s cruel possessiveness. When Akito violently reacts to their engagement, Hatori is permanently injured, losing the sight in one eye. Following this trauma, Akito berates Kana, convincing her that she is to blame for the injury. Overwhelmed with guilt, Kana falls into a deep and debilitating depression, unable to live a normal life. To save her from this suffering, Hatori makes the excruciating decision to use his ability to erase all memories of their time together as a couple.

Key relationships define her character. Her romance with Hatori Sôma is the most significant, described as a profound and loving connection that was cut short by tragedy. The depth of his affection is shown when he sacrifices his own happiness to heal her. Another important relationship is her friendship with Mayuko Shiraki, a college friend who remains a constant source of support through her depression and beyond. In the present timeline of the series, Kana has had her memory erased and is engaged to a man unrelated to the Sôma family. When she happens to see Hatori, she feels a slight awkwardness, recalling only a faded memory of what she believes was an innocent, unrequited crush. She is genuinely happy in her new life, and Hatori, upon seeing this, finds peace in his decision.

Kana’s development is one of a vibrant, hopeful young woman who is broken by a cruel act, only to be saved through sacrifice and allowed to live a new, happy life free from the Sôma curse. She does not possess any supernatural abilities. Her most notable characteristics are her profound empathy and the emotional strength she demonstrates by accepting the curse, though this same open heart leads to her eventual breakdown. She ultimately represents the theme of moving forward; she is able to leave her past behind and find a new beginning.