https://www.8ing.co.jp/museum/prd/gmaho/index.html
Using Google Translate, so I'll not be surprised if I missed some nuance. Or lots of nuance.
Anyway, here's what we have for starters.
--It takes place 54 years after Shippuu, using Miyamoto's ages for the guide. In the page for the secret characters, it lampshades how Gain and Chitta don't seem to have aged. Unfortunately, I can't find pages that relate the second half of the stages, so any clue in Tsumujimaru's return--if this isn't some Tsumujimaru II grandson of Hayatemaru--is sight unseen.
--Solo-Bang isn't so much greedy, as he's laser-focused on restoring his family's prosperity. Despite being the only member of his family left alive after their estate burned down when he was 5.
--Karte doesn't use a sorcer-striker. Rather, she has a bond with a dolphin-like creature that lets her fuse with them as needed. I guess the fused entity is Nirvana-sized?
--Miyamoto's technically a rounin now.
--The Grimlen...eep. A trio of 11-year-olds. Employed by an Association infamous for technically solving various crises, but usually leaving the area so barren that even mandragoras won't grow there for some time. Still like chocolate the most, and violence the least. Heavy destruction probably isn't that bad when it's necessarily aimed squarely at Underground Gobligan and its imperial ambitions, but I have a nasty feeling that Bornnham (a) isn't dead, (b) founded the Association so he could have his dirty work done while pretending to be dead, (c) isn't above beguiling children and who-wants-to-know-whom-else into doing his work, and (d) is tied with the Underground Gobligan Emperor for foremost suspect of killing Solo-Bang's family. Sending the Grimlen to fight Underground Gobligan would be Bornnham just wanting quick rid of a rival for planetary rule.
--Interesting tidbit for Golden in the secret characters page. His telepathy evidently causes his dreadful visage...maybe. The page questions if his eyes really are horrendously ugly. I wonder if what's actually going on is some sort of psychic feedback--looking into his eyes results in looking into your own thoughts. All of them, sublimated included...