"Watashi wa Knife" was written by Gorō Matsui and composed and produced by Tsugutoshi Gotō.

[1] Lyrically, the song describes a protagonist proclaiming herself to be a metaphorical knife "starved" for love and willing to measure up to a rough lover.

During the promotional cycle for Super Best, Kudo revealed she doesn't like the title of the song.

"Watashi wa Knife" received acclaim for Kudo's upfront vocals, as well as the song's "hard" hook culminating in an "epic" chorus, which were noted for producing an efficient change of pace and making the song memorable.

[1] Matsui and Gotō were praised for their practiced collaborative songwriting abilities.