The Great B-shot

(This was set after Cross Fight B-daman.) Few days after the battle with Dragold, Subaru received a letter from someone who had gone for 5 years. She wants him to find her, but in order to do that, he need help from others. But, can he do it? If so, can they find her? More importantly, who is she?
(I don't own Cross Fight B-daman or any other that involved in it. I just own this story.)