2003–2006: Decline in sales

In 2003, Hamasaki released three singles, "&", "Forgiveness", and "No Way to Say". To celebrate the release of her thirtieth single ("Forgiveness"), Hamasaki held the A Museum concert at the Yoyogi National Gymnasium. Her mini-album Memorial Address (December 2003) was her first album to be released in CD+DVD format in addition to the regular CD-only format.
Memorial Address topped the Oricon chart and became a million-seller. The sales of Hamasaki's singles began to wane, however: though all three of the album's singles topped the Oricon charts, "&" was Hamasaki's last single to sell over 500,000 copies. By the end of her Arena Tour 2003–2004, Hamasaki had become dissatisfied with her position in Avex: she felt that the company was treating her as a product instead of a person. Along with her dissatisfaction with her last two studio albums (which she thought had been rushed), this led her to begin work on My Story (December 2004) early. In contrast with her previous albums, My Story had no set theme, nor did Hamasaki attempt to write "something good" or even "something that would give people hope"; rather, she simply wrote freely and honestly. As a result, the album contained mostly autobiographical lyrics about her emotions and reminiscences of her career. She was so pleased with the result that she declared My Story the first album she felt satisfied with. My Story and its singles, "Moments", "Inspire", and "Carols", all topped the weekly Oricon charts; moreover, My Story became another million-seller. From January to April 2005, Hamasaki held the nationwide My Story arena tour, her first tour based on an album.
Miss)understood (January 2006), Hamasaki's seventh studio album, showed new musical directions. Wanting to sing a tune like those of Sweetbox, Hamasaki obtained the permission of Sweetbox composer Roberto "Geo" Rosan to use demo songs he had intended to use in Sweetbox's upcoming album. She edited the songs to fit her personal vision, rewriting the lyrics and rearranging some of the songs. The result was more musically diverse than the previous album; (Miss)understood included ballads, funk, dance-pop, R&B, and rock songs. All of (Miss)understood's singles reached the top of the Oricon; "Bold & Delicious" became Hamasaki's twenty-fifth number-one single. "Secrets" was, appropriately, the theme of Hamasaki's eighth studio album, Secret (November 2006). The album also explored strong female figures, love, and sadness; songs depicted the artist's struggles and "cheered on girls". Although Secret was originally intended to be a mini-album, Hamasaki "began brimming with things to say" and wrote five more songs. The album consisted mostly of rock songs and ballads; to complement these, Hamasaki experimented with new vocal techniques. Both of the album's singles, "Startin'" and "Blue Bird", continued her streak of number-one singles: "Startin'" became her twenty-sixth, setting a new record for most number-one singles held by a solo female artist. The album also topped the Oricon weekly charts, making Hamasaki the only artist to have eight consecutive number-one studio albums. Her sales, however, continued to decline: Secret was her first original studio album not to become an RIAJ-certified million-seller.