Since it's from POV of the guy telling it, we don't get to see the specific details on Shiori side and instead mostly see from the adventurers sighting of Shiori whenever she's in town.
First is finding her, the usual getting isekai'd, not knowing the language, the shock of realizing it's a different world, slowly getting used to life in new world, etc.
After realizing Shiori want a 'place where she belong' the old guild master introduced her to Akatsuki party, convincing her that 'isn't it about time you find a place of your own?'
A few months after they started, one of the adventurer felt like there's difference in quality of equipment between Shiori and the rest of the party.
Then she started looking rather lifeless, started avoiding people, even when shopping there's someone with her as if to keep an eye on her etc.
Then suddenly they learned that Shiori canceled her stay at her current abode, and the landlady didn't know where she went after that either.
Worried, they snuck into the guild to check on documents.
Turns out all these time, ALL of Akatsuki's spendings has been shouldered by Shiori alone.
They also left her out of the quest completion report, meaning while the rest of the party are A ranks, she's still D rank.
They likely have been threatening her with something that kept her quiet.
They even have her take out loans with the help of the guild, which makes them realize the old guild master was in cahoot.
But the party is not in town, so they can only wait.
When they came back, Shiori wasn't with them.
Obviously they confront them about it.
But Akatsuki told them she suffered a fatal wound during their retreat from the latest quest, and they didn't have the chance save her and so only could left her behind.
But later on someone came to report that Shiori is at the gate, wrapped in a slime that seem to be protecting her (yes, that's Ruri)
Basically while she was left in the dungeon, Shiori managed to befriend/tame Ruri who then carry her out to town.
Obviously there was no 'fatal wound' that Akatsuki claimed she suffered.
In essence, after they've used her to the point she collapsed, they just left her in the dungeon.
After pressuring, one of the party member who had a crush on Shiori confessed.
Kinda skimmed over that bit but something about nobles being involved.
Anyway, in the end the old guild master was replaced, and Akatsuki without Shiori's support kept failing quests afterward and now they're no longer around.
