"O.O" was written by Dr.JO (153/Joombas), composed by EJAE along with Brian U, Enan, MarkAlong, Charlotte Wilson, Chanti, Awry, Ayushy, Jan Baars, and Rajan Muse from The Hub, and arranged by the former three. was described as a song with "mixture of baile funk, teen pop, and pop rock" genres with "intense captivating trap intro". The A section of "O.O" was composed in the key of E minor, with a tempo of 133 beats per minute, and the B section was composed in A major with a tempo of 100 beats per minute.
