Kadokawa opened a website on Saturday to reveal a new anime project titled Isekai Quartet . The anime will be "broadcast" in spring 2019, and will be a crossover series featuring characters from the Overlord, KonoSuba – God's blessing on this wonderful world!!, Re:ZERO -Starting Life in Another World-, and Saga of Tanya the Evil franchises. The anime will feature the characters in super deformed form.

Minoru Ashina (Kaiju Girls, Pure Pure Purea Desu Overlord shorts) is scripting and directing the project. Minoru Takehara is serving as both character designer and chief animation director. Studio Puyukai (Kaiju Girls, Lord Marksman and Vanadis, Pure Pure Purea Desu Overlord shorts) is animating the work.

In the anime's story, a mysterious button suddenly appears one day, and characters who press it are taken to a new world to gather.

The announcement for the work stated that all four franchises together have more than 16 million book copies in print, and more than 500,000 combined Blu-ray Disc and DVD sales totals. All four light novel series are in the "isekai" (another world) genre, and each has inspired manga and anime adaptations.

Sources: Isekai Quartet anime's website, Kadokawa Anime's YouTube channel