What are the chances of 2nd season inlcuding arc 5?

OrdepNM said:
Actually, the calculations aren't so clear cut, as the later volumes of Arc 4 increased the page count by quite abit. Consider Chapters rather than Volumes: Season 1 adapted 47 chapters of the series (15 for Arc 1+2, 32 for Arc 3). Arc 4 has 40 chapters, meaning it's only 7 chapters short (or 15%) of the amount of ground S1 covered. Also adapting arc 5 this season would blow up the chapter count to 68 chapters, 44% more than S1 covered, which is alot.

Also consider that before adapting Arc 4, the show will need to adapt the Arc 3 epilogue, which ends in a cliffhanger that will certainly serve as the end of episode 1. Meaning that Arc 4 proper only starts getting adapted by episode 2.

Some extra things to consider: Arc 4 is very plot heavy and dialogue heavy, rather than action heavy so it'll be harder to abridge. Also, as you noted, the author already trimmed Arc 4 considerably by removing alot of the fat, merging loops, etc, meaning that further trimming for the anime will have to be done sparingly as what's left is already pretty focused. Cutting much more can gut the series progression as there's just no low hanging fruit for that.

The LN illustrator for the series published a commemorative illustration when the series was picked up for S1 (https://i.imgur.com/p1UcAOJ.jpg). For S2 he's done the same (https://i1.wp.com/anime-tldr.com/wp-content/uploads/ReZero-WP2-O.jpg) I bring this up because while the first image has all the cast for Arc 1-3, the second only has the characters that appear in Arc 4. We don't know for sure how much Otsuka-sensei knows about the anime production, but given how he released this image on the day of the S2 annoucement, it's likely he knows at least something and that the omission of any Arc 5 characters was deliberate.

Also, the ending of Arc 4 isn't one you can just pick up from next week. I'll be vague due to spoilers but it's very much a season finale that calls for a break of some kind. Following up with the first episode of Arc 5 in the following week would be... very awkward IMO.

All this to say: Well, of course they can rush this to hell and back and cram both arcs in 1 season, but it'll be a disaster if that happens. Rather, I'd say that S1 had 26 episodes (ok 25 but one was double), 85% of 26 is 22, plus one more for the epilogue puts it at 23, 1 short of a 2-cour 24 epiosdes run. This leaves a possible Season 3 of 1-cour to adapt Arc 5, which at 5 volumes and 28 chapters, is of similar length to the material covered in the second cour of S1 (5 volumes, 27 chapters) and is a much more action-focused arc than 4, which is easier to shorten for time.