Produced by the band's manager Kobametal, the record is a concept album of an "odyssey to the Metal Galaxy" and contains elements of music from various parts of the world.

Due to Yuimetal's poor health, the band performed with one backup dancer to form a trio alongside Su-metal and Moametal.

Metal Galaxy received generally positive reviews from music critics, and managed to peak at number three on the Oricon Weekly Chart with first-week sales of 73,096 units.

[15] Kobametal stated that he wanted to create Babymetal in the image of the cultural diversity found around the world in music, with Metal Galaxy being a "conceit to explore this idea".

The album also features guest musicians, including gruff growls by Sabaton frontman Joakim Brodén on the track "Oh!

[18] The first set of shows, Babymetal Awakens, was performed at Yokohama Arena and with a dancer taking Yuimetal's place.

Three support dancers—Kano Fujihira, Riho Sayashi, and Momoko Okazaki—officially termed the Avengers, took turns filling Yuimetal's role in the original trio formation.

[20] Titled as Metal Resistance Episode VIII, the era of Babymetal features a theme that the Avengers are said to be summoned by the Fox God.

and the band's subsequent performances at Yokohama Arena on June 28 and 29,[23] Babymetal revealed the title of the record to be Metal Galaxy.

[24] The Metal Galaxy World Tour began in the United States on September 4, 2019,[23] and was scheduled to conclude in Taiwan on April 3, 2020.

[25] The band's performance at The Forum near Los Angeles on October 11, 2019, coincided with the worldwide release date of Metal Galaxy.

[26] On December 4, 2019, Babymetal announced another European leg of the tour, including an appearance at Download Festival in the United Kingdom.

"Starlight" was released digitally as the second single from the album on October 19, 2018,[41] prior to the Japanese leg of the Babymetal World Tour 2018, and coinciding with Yuimetal's official departure from the band.

[3] Jason Pettigrew of Alternative Press called Metal Galaxy "striking in its abject weirdness", highlighting "In The Name Of" as "the best metallae-ton jam you've ever heard ".

[55] Sarah Shodipe of The Line of Best Fit praised the opening track "Future Metal" for bringing "grandiose, soaring moments", but criticized "Oh!

[57] Grayson Haver Currin of Pitchfork called the record "an exultant, near-absolute mess", and, aside from the highlights of "Kagerou" and "Shine", an "embarrassing gimmickry".

[67] In the United States, Metal Galaxy debuted at number thirteen on the Billboard 200, becoming the highest-charting Japanese-language album in the chart's history, selling 28,000 copies in its first week.