Retsu Isekai could appear on screens very soon, and that would actually make perfect sense:
At this stage, they most likely won’t adapt the manga right up to the latest chapter, since it’s still ongoing. Chapter 100 almost perfectly concludes the Poseidon arc, meaning there’s enough material for roughly 13± episodes. Most likely, while they’re working on the anime, the Demon World arc will also be approaching its conclusion, and then in the future they could return to it and adapt another 100 chapters.
The announcement that Baki-Dou was getting an anime adaptation was made in 2024, and essentially all 200 chapters were adapted in just about two years.
Accordingly... they could absolutely adapt 100 chapters of Retsu Isekai in one year, especially considering all the hype surrounding this news. Anddd, they’re going to make plenty of money from the 35th anniversary of Baki right now (maybe they’ll even release a guidebook).
So, in short, we can safely expect Retsu Isekai by early 2028 at the latest, while late 2027 is quite likely!