Hiroko Iizuka is a middle-aged actress who first portrayed the character Mio Hongo in the original version of the drama Tsukigomori. Years later, she is cast in the role of Mio's mother for the drama's remake, titled Dark Moon. Her age is presumed to be in her late forties.

In terms of personality, Iizuka is characterized as an old-fashioned and biased woman, particularly holding harsh attitudes toward newcomers in the entertainment industry. She is rumored to be stern with younger talents and is openly critical of those she deems inexperienced or unworthy. This prejudice is especially evident in her initial treatment of Kyoko Mogami and her dismissive view of the young director Hiroaki Ogata, whom she considers unreliable compared to his famous father. Despite this, she holds great respect for established and veteran actors like Ren Tsuruga.

Her primary motivation stems from a deep sense of pride and territoriality over the role of Mio Hongo. Having played the character in the original production, she feels a powerful personal connection to it. Her identity as an actress became so intertwined with the role that her name became almost synonymous with Mio. She is fiercely protective of this legacy and views the new production, particularly an inexperienced actress taking on her iconic role, as a potential contamination of something she holds dear.

Within the story's Dark Moon arc, Iizuka serves as an initial antagonist and a formidable obstacle for the protagonist, Kyoko Mogami. At the drama's press conference and early filming, she challenges Kyoko, demanding that she prove her understanding of Mio's character. She attempts to make things difficult for Kyoko, questioning her abilities and criticizing the director's decision to hire her. Iizuka even asserts her right to veto Kyoko's casting if her performance does not meet her standards. Her key relationships during this arc are defined by this conflict. She is at odds with Kyoko and Director Ogata but is an ally of sorts to Ren Tsuruga, whose opinion she values greatly. On set, she plays the mother of Kyoko's character, a dynamic that mirrors their real-life generational and professional tension.

The character undergoes notable development as filming progresses. During a crucial acting test, Iizuka tries to force Kyoko into replicating the original, more reserved interpretation of Mio. However, she is overwhelmed and outdone by the intensity and intelligence of Kyoko's radically different portrayal, which reinterprets Mio as a proud and defiant heiress who flaunts her scar rather than hiding it. In a significant moment, Iizuka publicly admits defeat, surprising the rest of the cast by conceding that Kyoko's new version of Mio has surpassed the original. She acknowledges Kyoko's talent, demonstrating that beneath her stubborn pride lies the ability to recognize and praise genuine skill.

Regarding notable abilities, Iizuka is a highly accomplished and respected actress, evidenced by the enduring popularity of her original performance as Mio. Her interpretation of the character was so impactful that it became the standard for the role, praised for its subtlety where Mio was a shy, quiet, and emotionless girl who used her hidden scar for a wounded gazelle gambit. Her version famously used peek-a-bangs in her hairstyle to conceal the character's facial scar. This original portrayal demonstrated a mastery of nuanced, reserved acting, which stands in stark contrast to the more flamboyant and intense acting style she confronts in the remake.