Nina to Usagi to Mahou no Sensha

During the war, people with magical ability were used to power magical tanks by biting on various magic plates. After the war was nominally over, rogue magic tanks still wreak destruction everywhere they go. Little Nina, after spending years being forced to use her magic to power a tank used to fight these rogue tanks, has become homeless and starving. When she attempts to steal food, she runs into a group of girls that are driving their own tank. Rather than hurt her, they take her into their home.

The group of girls comprise a private tank squad, called "Rabbits," which fights to defend their town from rampaging rogue tanks. After taking so much abuse in the past, Nina is understandably skeptical of the kindness the "Rabbits" show her, but she soon realizes that they can actually be trusted. Nina becomes the newest member of the Rabbits tank squad, dedicated to using her strength to protect others!

(Source: MangaHelpers)