Akane Isshiki is the main protagonist of the story, a fourteen-year-old girl living on the island of Izu Oshima. She resides with her younger sister, Momo, and her grandfather, Kenjirou, a scientist. Because her mother is hospitalized and unable to work, Akane has taken on the responsibility of supporting her family financially. She holds a part-time job as a newspaper courier, for which she rides a unique flying bicycle created by her grandfather.

Akane is defined by her cheerful, energetic, and optimistic personality. She is a classic Genki girl, rarely seen without a bright and positive demeanor. Her friendly and open nature leads her to be affectionate with both close friends and recent acquaintances, and she acts as a nurturing older sister figure to Momo despite her own occasionally ditzy behavior. She can be impulsive, often acting before thinking, and has a tendency to cause minor accidents due to her headstrong approach. One of her most notable quirks is her love for mayonnaise, which she puts on a variety of foods, including rice. Another distinctive trait is her unusual, goat-like laugh.

Akane’s primary motivation is to protect her peaceful world and the people she cares about. When an alien threat known as the Alone emerges to attack the Manifestation Engine, which provides the world's energy, her grandfather entrusts her with the key to the Vivid System. This system allows her to transform into a warrior named VividRed to combat the Alone. Her motivation extends beyond just fighting; she is driven by a desire to befriend and help others, even those who appear to be her enemies. Despite having a chronic fear of heights stemming from a factory explosion seven years prior that killed her father and severely injured her mother, she overcomes this trauma to fulfill her role, which is essential as most battles take place in the air.

In the story, Akane serves as the heart and center of the team. Her role is not just as a fighter but as the emotional glue that brings other characters together. A key aspect of her abilities is the power to perform a Docking Operation, which allows her to merge or fuse with another person to create a more powerful form. This process is typically initiated by a kiss on the forehead. As VividRed, her primary weapon is a boomerang-like tool called the Naked Rang. She is also naturally athletic, having learned kendo from a young age, which allows her to hold her own against skilled opponents even without her transformation.

Akane's most significant relationships are with her fellow Vivid System users. Her closest friend is Aoi Futaba, and the two share a deep bond, often described as a red oni, blue oni dynamic where Akane is the passionate and lively counterpart to Aoi's more reserved nature. She also builds strong connections with Wakaba Saegusa and Himawari Shinomiya, who join the team as Vivid Green and Vivid Yellow, respectively. A pivotal relationship is with Rei Kuroki, a quiet and initially antagonistic girl who is secretly helping the Alone. Akane’s persistent kindness and refusal to give up on Rei, even after learning the truth, are central to the story’s resolution.

Throughout the narrative, Akane undergoes development primarily by confronting her past. She actively overcomes her debilitating fear of heights, which is a direct result of the childhood accident that shattered her family. Her unwavering belief in friendship and her ability to forgive also prove to be a transformative force, not just for herself, but for those around her, most notably Rei. Her signature ability is the Vivid System transformation, which grants her a Palette Suit and the power to fight the Alone. Her most notable technique is the Vivid Punch, an elemental attack that utilizes the Power of Creation. She is also capable of achieving an enhanced state known as the VividRed Operation form.