“Mixtape: OH” is an emotional mid-tempo track marking Stray Kids return from an eventful first half of 2021. Its Korean title “애” holds a dual meaning: one being a youthful form used to mean “kid” and another meaning “love” (愛), implying they are still “kids in front of love.” It is the third installment in their mixtape project, following “Gone Days” in 2019 and “바보라도 알아 (On Track)” in 2020.

The release was a complete surprise, with no affiliated teasers, other than concept photos released after the song. This is was because it marked the surprise return of Hyunjin who had been on hiatus since February 2021, whom JYP Entertainment confirmed shortly afterwards that he would be returning to group activities starting in July. In the time he has been on hiatus, Stray Kids won MNet’s Kingdom: Legendary War and gained many new fans. With this release, new fans got their first taste of the group complete as eight.

Hyunjin also designed the cover art, posting other lollipop sketches for fans:

Despite not being a promoted single, “Mixtape: OH” earned Stray Kids topped Billboard’s World Digital Song Sales chart the week of July 10, 2021 – marking the group’s first No. 1.