The setting of this series is very interesting. The facility Sheena is in is one that accepts those without families and trains them to send them to war. Pretty fucked essentially to train child soldiers. For each one, they each have a certain amount of magical ability, and that is trained. Since this is innate from when you are born, this isn’t something that can be changed in terms of their potential.
The two leads, Sheena and Mimi, highlight this. Mimi clearly has high potential in combat, while Sheena has her struggles. Still, the contrast is that Sheena is quite the normal girl, and Mimi’s life is anything but normal.
While we see that kissing, which is basically how you give mana is how you heal. Which shows how talented Mimi is since she can do that. The way she can heal herself makes you wonder if she is human. Still, both girls each have their own loneliness differently.