Luna Nozawa is an aspiring fashion designer who moved to Los Angeles from San Francisco to take an internship position at legendary design house Forrester Creations. One of Luna's first assignments was to bring materials to veteran designer Eric Forrester. Eric's grandson, R.J. Forrester, took a shine to Luna, but Luna received repeated calls from her mother, Penelope "Poppy" Nozawa, insisting that Luna quit her job at Forrester. Luna continued getting to know R.J. and confided in him about how she and her mother were artistic types, while her grandfather and aunt were much more austere. Luna was warned by Poppy that her sister, Luna's aunt Li Finnegan, would not want Luna anywhere near the Forresters. Luna readied to resign when Li discovered her at Forrester, but with R.J. at her side, she stood her ground against her aunt; afterwards, Luna and R.J. kissed. Luna reunited with her cousin, John "Finn" Finnegan, whom she'd been separated from for years, and consoled R.J. when he took her into his confidence and told her that Eric had been given six months to live. Luna supported R.J. as Eric underwent an experimental treatment that saved his life.

Luna got a note asking for a dinner date that she assumed was from R.J., only to discover R.J.'s cousin, Zende Forrester Dominguez, when she arrived. Luna gently turned the interested Zende down. When Poppy came to town for an extended visit, Luna began asking Poppy to tell her who her father was; due to Poppy's continual refusals, Luna threatened to have tests done, which upset Poppy. After Poppy ran into Bill Spencer, Jr., whom she'd had a fling with some 20 years earlier, Luna agreed with R.J.'s assessment that Bill might be her father, which Poppy vehemently denied.

Luna lost her virginity to R.J. after he rented his own house. Like her mother, Luna liked to take mints, but Luna didn't know that Poppy's mints were infused and accidentally brought a box to a party she was attending with R.J. at the Forrester mansion. Having taken an excessive amount of the "special" mints along with alcohol, Luna began to feel unwell and excused herself, ending up in Zende's bed and making love to him, though she thought she was spending the night with R.J. Luna was horrified when she woke up next to Zende, and when she explained to Poppy what had happened, Luna came to realize that she had gotten high from Poppy's mints. Luna angrily accused Poppy of drugging her, but reluctantly agreed not to tell R.J. what had happened with Zende; Luna became nervous around R.J., repeatedly telling him she loved him and that she was afraid of losing him. Luna lamented that she didn't have a father to confide in, so when Bill arrived, she allowed him to comfort her; despite Poppy's protests, Luna still shared Bill's contention that she might be his daughter.

Becoming increasingly stressed over keeping her night with Zende from R.J., Luna finally confessed her mistaken sex with Zende to R.J. and was disheartened after R.J. wanted to take some time away from her to process the inadvertent betrayal. A few weeks later, Luna was overjoyed when R.J. forgave her and wanted to move on; however, Luna began feeling sick and took a pregnancy test. Unable to view the result herself, Luna had Poppy reveal it to her and was relieved to learn she was not with child.

Luna was surprised when Poppy finally began hinting that Bill really could be Luna's father. Luna watched in anticipation as the antagonistic Li, a doctor who distrusted Poppy and felt Poppy was lying about Luna's paternity, personally ran a DNA test; Luna celebrated with Bill and Poppy when the test did indeed reveal that Luna was Bill's daughter. The wide-eyed Luna couldn't believe it when Bill had her and Poppy move into his palatial mansion, nor when Bill decided he wanted to formally adopt Luna and make her a Spencer.

When Poppy's former lover, Tom Starr, and his co-worker, Paul "Hollis" Hollister, both died having overdosed on the same drug, Luna watched in horror as Poppy was arrested due to the police discovering a backpack in Poppy's apartment that was filled with the drug and Tom's letter's claiming that he was Luna's father. With Luna's paternity again in question, Luna agreed to take another test, which revealed she was not Bill's daughter; distraught, Luna kissed Bill. When Luna kissed Bill a second time, she realized she was being watched by Forrester's co-CEO, Steffy Forrester. At Poppy's place, Luna offered the confrontational Steffy a drink, which knocked Steffy out; Luna then proceeded to build a cage around Steffy.

Once Steffy awoke and screamed for help, Luna taunted Steffy and said that the building was empty and scheduled for demolition. Luna revealed her deeds: resentful of her flighty mother and the unstable childhood she'd had, Luna used the attraction between former lovers Poppy and Bill to plant the seed that Bill might be Luna's father, then bought a false positive test on the dark web that she switched with Li's accurate test. Luna had fatally drugged Tom to keep secret the fact that he was her real father, and Hollis, who had stumbled upon Tom's confessional letters; Luna had also framed Poppy by planting Tom's backpack in the apartment for the police to find so she could have Bill for herself, since Bill could offer Luna the life she deserved, unlike "sweet" R.J.

Luna further implicated Poppy by telling the cops that Poppy had confessed to Luna about killing the men. With Steffy locked away, Luna continued to work on Bill but was startled by an interruption from Finn, who had come looking for Steffy – Finn's estranged wife.