This is a list that ONLY includes all these isekais' chibi content done by Studio PuYUKAI, and the Isekai Quartet series that relates to said isekais. All of these are not necessary to watch Isekai Quartet. It'll be (almost) ordered by release, with each entry having the necessary shows / content listed to understand it, although it doesn't really matter much if all the people on this stack have likely already seen all of the shows included in Isekai Quartet.
Would I recommend going through it all? Not really, it's a big hassle to find everything. But I highly recommend this to any completionist like myself since it heightens the Isekai Quartet watching experience, or to Re:Zero fans when it comes to Break Time and Isekai Quartet, since there's a good amount of accompanying canon content as well as some big lore drops. But anyways, here's the list:
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