where did the quote of "in the end i cant say i hated mirabel" come from?
It's a translation of one of the lines from the end of Trails to Azure.
Explaining the entire setup would require spoiling like four separate games in the franchise. Obviously I can't explain it without your question itself giving away at least one twist antagonist, but she kind of sucks and her motivations make no sense anyways.
Still, I won't spoil anything else. Here's a short and otherwise spoiler-free explanation as to why we quote this all the time.
Trails/Kiseki has a lot of really bad habits that it does nonstop. Among them:
Refusing to kill anyone or commit to any serious consequences
Redeeming villains by telling you that you, the player, think they're cool actually. They weren't so bad. All those warcrimes they did? Those were just goofs. Funny gaffs between friends.
Two of the most egregious examples of these happen in rapid succession at the end of Trails to Azure, which we did a fully-voiced playthrough of alongside its prequel Trails From Zero. This character, Mariabelle, basically stabs a guy to death in front of you with magical javelins after spending two entire games doing a whole host of other awful things.
Even during the stretches of the game where she's meant to be your friend she acts like a freak and kind of a sex pest. She's not a very likeable character at the best of times, and at the worst of times she's War Crimes Annie.
The game ends with her turning to your party and going. "Oh, that guy I stabbed through the body ten times with spears? Don't worry, he's fine. I had the safety on." Then she teleports away and faces no consequences for any of the atrocities she did. She tells you she just got hired for an executive position at Club Terrorism and she goes to do that. The party then turn to each other one by one and all say some variation of "Y'know what, maybe she isn't so bad :)" when she is, demonstrably, absolutely that bad.
This is a reverse of another stock phrase of ours: "He loved you by the way".
We quote that one to make fun of bad writing that tells you about a relationship without actually putting in the work to make it feel real (bonus points if it's after the fact or the character is dead/sucked and they want us to like them retroactively).
"I can't say I hate Miriabelle" is the inverse, where the game is insisting that you loved the character. Didn't you? You did, right? I sure hope so because all the characters are going to act like you did.
Here's the moment in context for anyone interested, but please be aware if you click this you're going to be hit with spoilers for 120 hours worth of Trails games (but especially Zero and Azure)