Isekai Quartet

Isekai Quartet (異世界かるてっと) is an upcoming anime crossover spin-off that is set to air on April 10, 2019. It is a crossover anime series that will consist of characters from four major light novel works that boast a cumulative total of over 16 million copies in the total series, and boasting a total sales of more than 500,000 BD & DVD series: Overlord, Kono Subarashii Sekai ni Shukufuku wo! (この素晴らしい世界に祝福を！), Re:Zero kara Hajimeru Isekai Seikatsu (ゼロから始める異世界生活), and Youjo Senki(幼女戦記).

The series is produced by Kadokawa and the Studios in charge of animation will be Studio PuYUKAI. Asini Minoru will be the director/screenwriter; Takahara Minoru will be the character designer and general director. the latest news and information will be posted on the series official site. The opening theme for this is Isekai Quartet and ending theme is Isekai Girls Talk.

Summary
A mysterious switch appeared one day. When pressing it, they were sent to a different alternative world!! There are also characters from other alternative worlds gathered together...!?

Trivia

 * All four series possess the same theme of the protagonist being transferred to another world.
 * Staff who created Pure Pure Pleiades (ぷれぷれぷれあです), Re: PETIT ~Starting Life in Another World from PETIT~ (Re:プチから始める異世界生活), Youjo Shenki (ようじょしぇんき) will also be working on this joint animation series.
 * In lieu of a chapter from the Overlord Manga, the series was promoted in Monthly Comp Ace November 2018 Issue.