The track marked Hamasaki's increased creative control over her music, as it was the first song she composed, under the pen name "Crea".

Moreover, the single eventually sold over one million copies over its eighteen-week run and became a RIAJ-certified million-seller; "M" also won the Japan Gold Disc Award for "Song of the Year".

[2] She began work on an electronic keyboard; however, as she had little proficiency in the instrument, Hamasaki eventually resorted to singing the melody into a voice recorder.

Hamasaki is ambiguous as to the identity of "Maria"; however, she has stated that the song was inspired by a story told to her by a friend about a saint named Mary.

[3][4] The story was pivotal in the shaping of the theme of the song, which, according to Hamasaki, is about a "woman who won't change with time".

[9] The music video for "M", directed by Wataru Takeishi,[10] opens with Hamasaki singing the introduction against a stained-glass window.

When the first verse starts, the doors of the cathedral open and glowing particles sweep into the cathedral; at the start of the second instrumental bridge, the particles merge and Hamasaki appears in a wedding gown, at the intersection of the transept and the aisle, also in this scene she is wearing blue contacts.

He commented "It's a very chilled but introspective-sounding song (I can't be certain how introspective it is), a bit folksy at times but nice to listen to, plus it has some wild guitar work later on, reminiscent of Guns 'N Roses of olde."

[13] Michael McCarthy of Lollipop said that Hamasaki's delivery is intense and emotional in "M' and the rest of the record's ballads.

[27][28] By the end of 2001, "M" was ranked at number two on Oricon's annual singles chart, just behind Hikaru Utada's "Can You Keep a Secret?

[32] The song was aired extensively as a commercial song for TU-KA, in which she appeared, and a "limited edition Ayu model" leopard print cell phone was released in honor of the leopard print she had shown on the jacket of "Surreal" from Duty released three months earlier.

[36] She also appeared on a TV program at the time wearing an image of the Virgin Mary as she did in her music videos and jacket.