On May 7, a mysterious video featuring Kara's member Goo Hara was revealed on DSP Media's YouTube account with a male voice on the background.

On May 21, it was revealed that A-Jax was set to be the opening act in Kara's last two shows of their first tour, Karasia, in Saitama, Japan.

A-Jax has signed under the equivalent conditions that other Korean male idol groups, who have already established their popularity, have been given, making it an unprecedented event.

[3] On May 28, DSP Media released, on A-Jax's YouTube account, a teaser of the music video for their official debut song "One 4 U".

[13] Due to a problem with the choreography, the group decided to change it on its second week of promotions.

The choreography, called 'back down' dance, is falling on your back from an upright position while keeping your body straight without any safety devices.

All tracks are written by Steven Lee"Never Let Go" debuted at position number 164 on Gaon Chart, in the week of May 25, with 1,441,047 points.

[20] On June 19, Universal Sigma announced that "One 4 U" was re-recorded in Japanese and will be released as their debut single in Japan.

The b-side "Break Up" was written by Kenn Kato and composed by Kim Won-hyun, Shim Man-joo.

The first press edition of the single include a cover of the song "Crazy 4 U", originally sung by the boyband SS501.

The Japanese version of the music video premiered on the network Space Shower TV on July 6, 2012.