Seven Seas Entertainment announced on Thursday that it has licensed Fumihiro Kiso 's The Testament of Sister New Devil Storm! spinoff manga and plans to release the first single volume on September 26. The volumes will carry a mature rating, so they will be shrink-wrapped in stores.

Seven Seas also announced that it will make the original The Testament of Sister New Devil , Akuma no Riddle , Magia the Ninth , Please Tell Me! Galko-chan , and My Girlfriend is a T-Rex manga available as eBooks. The company plans to make all of its eBooks available globally in the future.

Seven Seas describes The Testament of Sister New Devil Storm! as a "comedy spinoff" where the "demonic step-sisters vie for more power and pleasure than ever before." The company's story description is as follows:

High school student Toujo Basara's life has taken a turn for the strange. Although hesitant about his father's sudden decision to remarry, he can't deny it comes with a couple perks—drop-dead gorgeous step-sisters...who also happen to be members of a demon clan! Mio Naruse is a Demon Lord and Maria Naruse her succubus servant. Chaos and passionate antics ensue as Basara gets acquainted with his new demonic siblings, trying to protect them from dangerous demon rivals and struggling to keep up with their lusty, devilish appetites.

The spinoff manga began in Hakusensha 's Young Animal Arashi magazine in February 2014, and ended in May 2016. Hakusensha published the fifth compiled volume in August.