Grimlock ♥ Ultra Magnus

Victorian!   A female combiner!   See, Arcee doesn't like that the Enigma of Combination exists.   It could potentially be used to change people against their will.   She had her gender swapped without her consent, and has been mad ever since: she described it as getting two sets of input - her original male set, and her new female set - which was torture for her.  

She left behind a trail of bodies trying to find the 'bot who'd done this to her, and kill him.   She was isolated, antisocial, and uncomfortable with herself and everyone around her for a very long time.   It's understandable why she'd want to destroy the Enigma.   Except that it's considered a holy relic by the Camiens, since it was left by a Prime, an original Prime.   When they defend Windblade, and try to stop the Enigma from being destroyed, well, some of the Camiens get too close.  They combine.   

And they try to kill Arcee.   There are hints that one of the combiners has a secret, and I hope this is explored in further comics.   This, however, was a one-shot so it will have to be one of the sister series.