Haru Kasukabe is the 16-year-old main protagonist in a 2034 narrative. A first-year high school student with reddish-brown shoulder-length hair and an average build, she is consistently energetic and sports a wide smile. Her name reflects springtime and sunshine. Standing 157 cm tall and weighing 46 kg, she is talented at cleaning and interested in singing and collecting keychains.

She debuted as an idol before joining Three Seven Studio but found no success, leading to resentment toward the idol industry. Her involvement began unexpectedly when she applied for a cleaning position at the studio. Persuaded to form an idol group, she returned to idol activities after encouragement from her younger brother, whose approval motivated her to pursue her dreams despite past disappointments.

As the first idol recruited under the new studio, she became a foundational member of 777☆SISTERS and its subunits WITCH NUMBER 4 and HARU☆JIKA. Her prior experience positioned her to assist in scouting members like Musubi and Rona. Within the group, she functions as a mediator, using her innate positivity to maintain cohesion and support fellow members during challenges. Her cheerful demeanor and reliability make her widely well-liked.

Her development centers on transforming from someone disillusioned with the idol world into a unifying force within the studio. This evolution is reflected in her growing popularity in successive in-game contests: 4th place in the 2022 vocalist-focused idol grand contest, 3rd in 2023, and 2nd in 2024. Her story emphasizes perseverance and reconciliation with past setbacks, framed by her commitment to not disappoint her brother.