"Tatta Hitotsu no Omoi" begins with the chorus, solely backed with stringed instrument-sounding synthesizer notes.

The bulk of the song is arranged with bass, piano and percussion sound effects.

Kokia felt that the song was created from having the challenge of writing something uptempo (specifically for the anime).

[4] Because of this, "Tatta Hitotsu no Omoi" is Kokia's fifth best selling single, after "The Power of Smile/Remember the Kiss," "Kawaranai Koto (Since 1976)," "Ai no Melody/Chōwa Oto (With Reflection)" and "Follow the Nightingale".

They praised the B-side "Umaretate no Shiro" for its "stress clearing harmony," and noted a Norse feel to the song.