It's Japanese title is Isekai no Sekishi Monogatari, and it's full English title is Tenchi Muyo! War on Geminar. It is part of the Tenchi Muyo multiverse but it stands on it's own just fine, you can tell by the titles how the localization was banking on that connection more then the original creators were.
I've been planning to write something on this now overlooked Anime's importance to the Isekai genre for awhile, well before this current "Jobless Reincarnation is the grandfather of Isekai" nonsense started.
When I started hearing this stuff about Jobless I was prepared to call BS even if it's LN release date was as recent as 2010. When I saw it was January of 2014 I went "........ have these people forgotten everything that came out before Konosuba and Re:Zero?"
Even when talking about a very specific kind of Isekai, Male Lead Harmey Medieval European Fantasy, this LN came out after Problem Children and Outbreak Company already had Anime. No Game No Life got it's Anime that same year and it's first LN came out in 2012, Overlord's LN also came out in 2012.
One video promoting Jobless as this secret progenitor of these trends said it's LN came out a month before Knosuba's beating it to the getting run over by a Truck at the start trope. Konosuba is a parody, the kind of parody that can only work if the tropes and genre conventions it is parodying have been entrenched for longer then a month. The author would have had to have been working on Konosuba already well over a month before it came out. Even if these are indeed the first two Isekai LNs to specifically use the run over by a truck prior to reincarnation trope, it's probably a coincidence.
Because using getting run over by a vehicle like that for the idea of death coming out of nowhere certainly happened before. In Anime it goes back to at least Minky Momo in the early 80s. Outside Anime it technically happens in Mean Girls in 2004 in a way that is Comedic like it is in Konosuba. I should also note that the last Narnia novel has the protagonists of prior novels die in a train accident. Also in the context of Meta Comedy Anime, Excel Saga began with the MC getting hit by a truck back in the fall of 1999.
What I mean by War on Geminar being the first "modern" Isekai Anime is how before then Isekai in Anime was still almsot exclusively Shoujo, with the most notable exception being El Hazzard which is still pretty far from the formula we post 2010s Anime viewers are used to. And even if you consider a certain type of VRMMO story to be at least a close cousin of the genre, none that truly look like SAO existed in Anime form prior to 2011.
War on Geminar was a 13 episode OVA series released from May 2009 to May 2010. And it being that old surprises me because it resembles the clichés and conventions and even aesthetics of the post 2016 Isekai scene so much it feels like something made specifically to be the Tenchi franchise's take on it like Pretty Sammy was for Mahou Shoujo. But instead it actually came before all of those.
But it is also in my opinion worth watching for it's own sake regardless of how it compares to anything else.
The first episode is pretty unique in how it completely forgoes one of the points of using Isekai as a plot device for a fantasy story, having the person from our world be the POV through which we the audience learn about the fantasy world. Instead it is told from the POV of people indigenous to this Fantasy world, doing it's world building like a non Isekai Fantasy story would, with the Isekaied character not even being the protagonist yet but an antagonist, an alien presence they need to figure out.
One of our main characters holds the title of Empress, and in the Dub at least speaks using the Royal We which I feel the VA handled perfectly.
Usually in SciFi and Fantasy stories if there is an Emperor or an Empire the real world inspiration is either Ancient Rome or 19th Century Brittan. And maybe some Nazi imagery thrown in if you want no ambiguity that it's an Evil Empire. However what interests me about War on Geminar is how this "Empire" actually seems kind of like the Holy Roman Empire.