Isekai Quartet

Isekai Quartet (異世界かるてっと) is an anime crossover spin-off that first aired on April 9, 2019. It is a crossover anime series that consists 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: Youjo Senki, 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 Overlord (オーバーロード).

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

So far, two seasons have been released, with a third on the way.

A Season 3, following the last title with Isekai Quartet 3, has been confirmed to be in production March 31, 2021. The season is introducing new characters from another series: Cautious Hero. It is speculated that the transfer students are only temporary, and last season's transfer students may not return.

Summary
A mysterious switch appeared one day. When pressing it, they were sent to a different world! In a desire to return to their home, Tanya and her comrades must go through High School classes. Tanya and her comrades figure out they aren't alone in the situation, as three other worlds were affected by this switch too. In the end, the four vastly different groups unite in order to return back to their old lives.

Trivia

 * The name of the show refers to 4 productions of the Isekai genre. This show is also an Isekai, as citizens of all four shows are put into a new, unfamiliar world.
 * When it comes to affected characters, the official number isn't fully known.
 * Staff who created Youjo Shenki (ようじょしぇんき), Re: PETIT ~Starting Life in Another World from PETIT~ (Re:プチから始める異世界生活), and Pure Pure Pleiades (ぷれぷれぷれあです) also worked together on this joint animation series.

Isekai Quartet