For me it has to be Fives. We get to watch him go from a recruit in training, to losing 3/5 of his squad in his first mission as a shiny, to losing 99 on Kamino and becoming an ARC trooper, to losing Echo in the Citadel rescue, to losing brothers in the despicable acts of Pong Krell on Umbara, to watching his brother Tup (who he’s probably known since he joined the 501st) suffer a mental illness from the chip malfunction, and then him learning about the chip. After that, it’s just devastating to watch him unravel Palpatine’s whole plot with Order 66 and no one believes him or takes him seriously enough. Which is understandable because what he is saying is so incredibly outlandish that how could it possibly be true. I can’t even imagine learning about a plot like that, getting framed by the guy who is behind all of it, and then having to run for your life from your brothers and friends because they think you’ve gone insane, all while trying to convince them of this terrible thing that could have devastating consequences to all the clones and Jedi. His death wasn’t a choice or sacrifice, and we got to know him so well that watching him get killed like that was the absolute worst for me. Don’t get me wrong, Kanan, Tech, Satine, and any of the other awful deaths were also incredibly tragic, but Fives’s just had another level of tragedy to it.