TV-Series
Description
Kotono Nagase is the younger sister of Mana Nagase, a rising idol star whose sudden death in a traffic accident left a profound impact. Following her sister's passing, Kotono, then a second-year student at Hoshimi Private High School, withdrew further into solitude despite never being particularly sociable. She channeled her grief into relentless solo practice, dedicating herself entirely to becoming an idol to fulfill her sister's unrealized dream. This intense focus, born from a fierce desire to reach the top and match Mana's perceived success, fostered a strict demeanor towards both herself and others.

Physically, Kotono is 17 years old, stands 162 cm tall, and weighs 43 kg. She possesses long black hair and velvet-colored eyes. Her signature image color is dark blue (hex #6088D0). Her typical idol costume features a navy blue and white dress accented with blue or purple laces, a white and blue/purple striped hair accessory, a long navy blue stocking with a frill on her right leg showcasing a star, sun, and moon anklet, a short stocking on her left leg, and blue and white high-heel shoes. She also wears white wrist bracers with dark blue lacing.

Kotono initially aimed for a solo debut, mirroring her sister's path, and resisted joining the new unit formed by Hoshimi Production. She eventually accepted the necessity, marking the beginning of her integration into Tsuki no Tempest, where she rose to become leader. This forced collaboration proved a significant hurdle; her solitary nature and initial coldness made forming bonds difficult. Her journey involved gradually learning to trust and rely on her fellow members, overcoming her tendency to isolate herself through shared hardships and collective goals.

Her development is deeply intertwined with relationships within Hoshimi Production. Nagisa Ibuki, her classmate and one of her few friends since middle school, offered crucial support. Sakura Kawasaki, whose voice resembled Mana's, became a significant figure; Kotono identified Sakura as a rival due to her unexpected talent and drive, yet their relationship evolved into one of mutual respect and motivation, pushing each other to improve. The collective effort of Tsuki no Tempest helped Kotono slowly open up, shifting her focus from a purely individual pursuit centered on her sister's legacy towards embracing teamwork and shared aspirations.

Kotono's motivations evolved throughout her idol career. Initially driven by a need to honor Mana and reach her perceived heights, her experiences performing with the group and confronting the realities of the idol industry—including its pressures and public scrutiny—led her to forge her own identity. Witnessing the performance of the rival group LizNoir prompted critical reflection on her own abilities and goals. By the series' conclusion, her focus shifted from solely surpassing Mana to creating her own path and connecting authentically with her audience through performances representing her own efforts and those of her unit.

Outside idol activities, Kotono enjoys gymnastics and history but struggles with mathematics and physics. Her favorite food is cotton candy, a preference rooted in a cherished childhood memory involving her sister at the Hoshimi Festival. She finds solace in quiet places, particularly the beach at night. She also once harbored a childhood dream of becoming a pianist, influenced by her mother, but ultimately chose the idol path because of her sister.