Micro Magazine’s Light Novel Imprint GC Novels official Twitter account on January 17th announced that the total print run of Fuse’s fantasy light novel series “That Time I Got Reincarnated Slime” and its various manga adaptations / spin-offs exceeded 30 million milestones.

The anime ‘s official Twitter account has also announced the news and confirmed a memorial campaign to celebrate the record of 30 million copies is now planned.
さらに!なんと!#転生したらスライムだった件 シリーズ累計発行部数が『3,000万部』を突破いたしました!!
— 【公式】アニメ『転生したらスライムだった件』 (@ten_sura_anime) January 17, 2022
日頃よりの応援、誠にありがとうございます。
現在記念キャンペーンを企画中ですので、お楽しみに!
杉P#転スラ #tensura pic.twitter.com/mxLvT8k8bw
That Time I Got Reincarnated as a Slime or Slime Isekai is a Japanese fantasy light novel series written by Fuse, and illustrated by Mitz Vah. The story is about a salaryman who is murdered and reincarnates in a sword and sorcery world as a slime with unique powers and gathers allies to build his own nation of monsters.
After being serialized online on the user-created novel publishing site Shousetsukani Narou, the publisher began releasing a printed version of the illustrated novel by Mitz Vah in May 2014. As previously reported, the series reached a record of 20 million copies in September 2020. This means that in 16 months, a huge copy of 10 million copies was added. The main reason for this tremendous increase in distribution is, of course, the success of the second season of TV anime, which aired in Japan from January to September 2021. The distribution of the series is expected to be further boosted by the next animated feature film. It will be released in the fall of 2022.
Source – GC Novels official Twitter & the anime’s official Twitter