Hi High

A teaser for the music video of the song was released on August 17, 2018, and showed the members of Loona running towards somewhere.[4][5] Various teaser images were also revealed in the lead up to the album's release.[4] On August 20, "Hi High" was released alongside the album + + as its title track.[2]

The lyrics were written by Jaden Jeong, MonoTree's GDLO, and MonoTree's Hwang Hyun. The music was composed by Mayu Wakisaka, MonoTree's GDLO, and MonoTree's Hwang Hyun.[6] According to Loona, "Hi High" has the double meaning of saying hi to the now-complete lineup of the 12 members in addition to representing Loona's goal of climbing to the top of the music scene.[7] It can also been seen as a reference to the LOONAverse, as all 12 girls, or 3 'worlds' come together. Billboard described "Hi High" as a "bright electro-pop song full of quirky beats and synths" with an "upbeat chorus".[3] Furthermore, Billboard stated that the "track picks up and drops momentum frequently", allowing it to highlight the different singing styles of each member of Loona.[3]

The Kpop Herald also commented on how the song "delivers the bubbly energy of the band",[2] and TenAsia similarly characterized the song as energetic.[8] Hong Dam-young's album review in The Korea Herald remarked that "Hi High" is fast-paced with a "vivacious tempo and explosive vocals."[9] However, Hong criticized the writing of the song's lyrics as a "major drawback" due to some of its "silly lines".[9]

"Hi High" peaked at number 11 on the US World Digital Songs Sales, marking their second consecutive entry on the chart as a full group.[10]

The song's release on August 20, 2018, was accompanied by a music video that was directed by the production company Digipedi, which also worked on many of Loona's previous music videos, including for "Favorite".[3] The video is colorful and depicts the members of Loona each dressed in a schoolgirl style, dancing and running.[2][3] At the end of the video, Loona member HeeJin jumps upward toward the sky, portraying a sense of positivity and enthusiasm.[11] The video also features the members wearing denim as they perform a routine in an industrial yard, while other scenes see the girls running through meadows, on swings, and jumping off roofs.[12]

The music video reached three million views in three days after its debut,[13] and it later surpassed ten million views eight days after its debut.[11][14]