Lim Young Min mentioned, "This album was released after 4 months and was released in a short period of time thanks to everyone's support in 'Unmix.'"
Kim Dong Hyun commented, "In our first mini album, we wanted to express our genuine selves. As for this latest album, we hoped to match up to our fans. We did our best to portray such feelings of joy and excitement."
The title track "Diamond Girl" features a funky, retro feel. The diamond also signifies MXM's official logo, expressing the duo's affection towards their beloved fanbase.
In regards to their promotion period overlapping with other artists from 'Produce 101' season 2, Kim Dong Hyun commented, "We receive a great deal of energy when we run into each other and I hope everyone succeeds"
Lim Young Min shared about fellow Brand New Music trainee and Wanna One member Park Woo Jin and said, "I didn't get much in contact with Woo Jin at the beginning...but now we are talking frequently...To be honest, Woo Jin is like a younger brother who contacts me and cheers me on. While Lee Dae Hwi and I talk more about music-related topics. He recently told me 'Diamond Girl' is exciting.'"