Machida submitted her work for the 2016 R-18 Literary Award, which is an annual juried prize for a story about a woman written by a woman. Jurors
Shion Miura and
Mizuki Tsujimura both selected Machida's
Cameroon no Aoi Sakura (lit.
The Blue Fish of Cameroon) as the grand prize winner. The story was included in her first book, a collection of short stories that was published by
Shinchosha in 2017 under the title
Yozora ni Oyogu Chokorēto Guramī (lit.
Chocolate Grammies Swimming in the Night Sky). For the next few years, she wrote approximately one novel per year, including
Gyoran,
Utsukushigaoka no Fukō no Ie, and
Konbini Kyōdai. In 2021 her novel
52 Hertz no Kujiratachi (lit.
52 Hertz Whales), a story about two troubled and isolated people who become friends that can communicate with each other despite their difficulties, won the
Japan Booksellers' Award Grand Prize. The title of the story refers to a
whale in the Pacific Ocean that calls at a frequency that other whales cannot detect. Writing for
Da Vinci, reviewer Yuki Mita observed that the core lesson of the book was positive despite the difficult situations faced by the characters, and that the book provided encouragement for people to keep trying to communicate until they find someone they can talk to. In
Real Sound, reviewer Ichishi Iida noted that the book had become a bestseller, and suggested that the story showed how Japanese society needed something like religion or another similar social force to generate and sustain relationships between people when other bonds fail. The book sold over 400,000 copies. Machida followed
52 Hertz Whales with her 2021 novel
Hoshi o Sukuu (lit.
Scoop Out the Stars), which she wrote to explore the concept of "parent gacha", the idea that one's fate is determined by one's family circumstances. Machida's 2022 novel
Sora Gohan continued the theme of mothers and daughters, following the story of a child named Sora whose relationships with other parental figures complicate her relationship with her birth mother. For reviewer Asayo Takii, writing in the
Sankei Shimbun,
Sora Gohan is "a story of a mother and daughter growing together". == Selected works ==