Beatrix is the equivalent of Hitler's foremost general. She devoutly charges on the front lines, slaughtering any and all opposition, intent on seeing the Burmecians purged from existence as her Queen commands, women and children included.  
Even the peaceful Cleyrans, sister race of the Burmecians who attempt to shelter the survivors of her genocidal campaign, are not safe. She attacks, mocks them for using a powerful object for something other than violence, then only retreats to allow her Queen to nuke them all into oblivion. Her only reflection on this is that she could have butchered them all herself.  
But no wait she's good actually because she can't betray the Princess who she is also sworn to, besides the Queen.  
Not that causes any reflection or regret for her past actions. No apology or consideration that killing children was a bad thing to do. But she's on team Good Guy^TM now so all's well! Everyone loves her and asks for her stellar advice when needed, war criminals being well known for their sage wisdom.  
Doesn't stop her from being a nasty bitch to her supposed allies and underlings who already willingly risk their own lives in the final battle, though.  
  
She is an insufferable writers pet. She gets two entire music tracks just for herself and her specialness. 
She forcibly defeats the player not once, not twice, but *three* times with cheap instakill attacks, just to flex in your face that she's just the coolest and best ever. Not even the actual villain of the game gets to do anything like that.  
One of the main cast adores and devotes himself to her and this is essentially the culmination of his arc, his arc that was about realising that blindly following his sworn knight's oath might be a tad questionable and not actually always the moral choice. The thing she absolutely *didn't* do herself. And by contrast, he scarce did anything wrong, seldom wholesale mass murder.  
The Burmecian on the squad, the Burmecian knight (who logically ought to be her equal imo), is part of the party of 4 that loses to her 3 times in a row, during her butchering of her people, and all she gets is a couple lines saying she won't forgive her the very moment Beatrix finally changes sides and... that's it for the rest of the story. After this Beatrix herself gets more 'character development', if it can even be called that. The rest of the cast just immediately forgive and forget everything she's ever done, which is easy as they scarce recognise she even did anything wrong to begin with. Nevermind the constant glazing of her by multiple characters in game.  
She even gets more screen time in the full CG ending than most of the actual main cast do, including being part of the finishing shot. Because of course.  
  
The depths of my hate are only furthered by seeing this character constantly glazed and adored by both the company the fanbase at large. She has action figures on par with actual main characters, and is the subject of mods adding her as a permanent party member, among a seemingly endless sea of popularity.  
  
She's a *genociding child murderer*.

Beatrix, enactor of genocide