Busou Shinki: Armored War Goddess

The story

High school student Masato has been living abroad and only now returning to Japan. On his first day at school, he is awoken by Ann, his Arnval model Shinki. As he hurriedly prepares to depart, Ines, an Altines model, and Lene, an Altlene model, both make their way out of the boxes they have been to neatly packed into. For the sake of their Master, they enthusiastically go about cleaning and squaring away Masato's belongings. In the midst of this, they come across a box labeled Valuable. What could be inside?