"...My dream was to become the world's greatest adventurer, together with Athena."
"... But... I got banished, and I hated you for it."
Est, you're forgetting that you saw Daru and Athena essentially going to town immediately after they kicked you out - THAT is what made you hate them.
It was a misunderstanding, sure, but Daru capitalized on that to keep you and Athena separated! Just say what happened and Athena will realize the truth, that Daru is a groomer and benefitted from having you killed or banished, and she'll go back to you!
"I learned that the reason for that was your kindness."
No, it was her incompetency as a leader and a fighter!
"And so, thank you."
"Thanks to you all, I was able to grow."
DO NOT THANK YOUR ABUSERS!
You were able to grow all on your own, quite literally!
You picked up their slack outside of the dungeons, by managing their inventory, cooking, lodging, money, etc., and even in the dungeons you still managed the items and buffed the entire party to make up for their lack of power and coordination!
Daru and Ravioli (or whatever her name is) are the ones who were perfectly capable of protecting the back lines and training you and Athena to be stronger but decided not to because of their egos! They were the ones holding you back, and Athena hasn't taken a single good decision this entire story!
It was all YOU, Est! You overcame those trials your former team irresponsibly put on you all on your own!
"The banishers have their own stories too."
"And this is... The story of the banisher's side."
A poorly written story, you mean.
Finally this crap is over. No wonder the LN got axed, this is just a glorification of abuse, grooming, victim-blaming and gaslighting, made by an author that does not understand what he's writing!
There's only been one other story that ever frustrated me to this extent, and precisely because it also glorified abuse due to the author also not understanding what he was writing - Metroid Other M.
And just like Other M, Tsuihou suru gawa no Hanashi will go down in history as a lesson on how NOT to write a story!