The events of Excella's story and especially her ending play out as a parallel to the fairy tale she loved while growing up.
While romancing Excella, she gives Yuma the 'Glass Slipper Sigil' at the beginning of her romance route. Later on in her route, she admits to fantasizing about being a commoner, just so that she could have been allowed to live a normal life with Yuma, the exact opposite of Cinderella's wish. And itcomes true.
Fridge Horror
The battalion fighting alongside Sonia in the prologue stay behind to Hold the Line, which is a dangerous task but one they sound confident about...and then a few minutes later, Excella unexpectedly arrives, with reinforcements (in the form of three giant dragomachina), to take control of the fortress. A Noble Demon she may be, but those soldiers are probably in prison. At best.
Which recontextualizes how desperate Sonia is to get Yuma's help the following morning. Not only were those soldiers her people, but the cutscene dialogue shows that she knew them personally.
