User blog comment:Omega natsu2/Chapter 355: Song of the Fairies, Predictions./@comment-7418318-20131005235352/@comment-7418318-20131006094015

I also wonder why Ymir would go back to assist Reiner and Berthold. Apart from a low chance of being able to help them (and survive) in the first place, do they really deserve being saved?

Sure they've been good comrades, but they knew full well that many people would be killed when they breached wall Maria and expected similar casualties when they attacked Trost. They even admitted to trying to wipe out the Humans living behind the walls.