LIGHTSUM, the Cube Entertainment girl group who debuted in 2021, have released the music video for 「どうして (Doshite)」, a Japanese-language track from the mini album 『Re:idol』. It went up on the group’s own YouTube channel rather than a distributor’s.

Re: at the front of a Japanese title comes from email

Japanese releases have long put Re: in front of a single word — Re:birth, Re:start, and here Re:idol. The prefix is read as the reply header on an email, the tag that marks a message sent back in response, and it drifted into Japanese pop culture as shorthand for doing something again or returning to it. Anime, games and record titles have used it for years, so audiences there parse it without thinking. It is a Japanese-market convention rather than a Korean one, which itself tells you who a record titled this way is aimed at.

About this release

「どうして (Doshite)」 is the official music video for a track from LIGHTSUM’s mini album 『Re:idol』, published on 23 September 2026. The official description carries no producer or songwriting credits and lists no featured artist — only streaming and purchase links, plus the group’s official accounts. The copyright line reads simply as LIGHTSUM.

Watching from outside Korea

The group runs two separate X accounts, cube_lightsum for general activity and LIGHTSUM_JP for Japan. Japanese-market releases are often announced only on the latter, and streaming availability can differ by country, so it is worth following both if you want the full schedule.

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