Mimi lets Sheena in on quite the notable secret that she is dead. Well, it’s a bit more complicated than that. Mimi’s mother revived her, and it seems that has notable consequences, where now Mimi is immortal, so in a way she is dead because she did die.
Not being able to die is quite the revelation, but Fran brings up a good point: thanks to Mimi’s mana so many are safe. At the same time, Mimi herself takes so many lives that, as a person, she is very lacking in that area. As Sheen grows closer to Mimi, the more she can’t help but feel sad for Mimi. Even the adults view her as an object or tool for war.
Still, Fran’s point is to counter taking away Mimi’s immortality in that the war is complicated. Mimi would still fight and finally die. In reality, it does nothing to help by conforming to Sheena’s ideals. The main issue is that Sheena is claiming what is right and wrong but not capable of doing anything due to her weakness.