Riina Tada is a 17-year-old Tokyo-based idol standing 152 cm tall and weighing 41 kg, with beige hair and aquamarine eyes. Her blood type is A, and her birthday falls on June 30th. She introduces herself aspiring to be a "rockin' idol" while confessing nervousness during formal presentations. Constantly seen with headphones, she passionately admires rock music and strives to project a "cool, rockin' idol" persona, though her initial limited exposure to the genre leads others to question her authenticity. Undeterred, she commits intensely to this ideal, undertaking guitar lessons under Natsuki Kimura to pursue genuine musical growth.

Her bond with Natsuki evolves from admiration into a mutual partnership, forming the unit Rock the Beat. She also collaborates in * (Asterisk) with Miku Maekawa and Masque:Rade with Karen Hojo, Miho Kohinata, Chieri Ogata, and Mayu Sakuma. With Mayu, she displays duality—reliably supportive yet occasionally acting spoiled around more diligent peers.

Riina lives with her parents and maintains close family ties. At school, she describes herself as reserved, contrasting her fervent stage presence. Academically, she crams for exams but rapidly forgets material afterward. She battles insecurity about her guitar skills, fearing they undermine her rock idol authenticity, channeling this anxiety into fierce determination.

Her speech shifts from formal language with the Producer and senior idols (initially omitting honorifics) to using "-san" for the Producer as a sign of earned trust. During recordings like the "Idol Challenge for Two" event, she demands multiple vocal takes to achieve perfection, driven by her goal to "surpass herself."

Her theme color is royal blue, reflecting her Cool idol classification. Beyond rock, she enjoys exploring broader music genres.