Mahou Shoujo Kokone wa Kakukatariki

Mahou Shoujo Kokone wa Kakukatariki (魔法少女ここねはかく語りき) is a manga series by Nanaroku. It was serialized in Dragon Age.

Plot
I met a magical girl; and so began my story...

"Then I will become a magical girl !" In order to save Hoshi Karen, the magical girl who had protected her even while being pursued by tanks, Kokone, who was entrusted with Karen's Grimoire, decides to become that which is acknowledged as a "Calamity" by the world... A magical girl!