BBK/BRNK - Season 1 Episode 3 Heart and Limbs

Ten years ago, many Buranki fell to Earth and were destroyed by Banryuu Reoko and her Buranki, Entei. That was the day Reoko and Entei's reign of terror began. In the present, Azuma and his companions flee Shinjuku and meet a woman named Horino, who tells Azuma that his mother was the only person who ever defeated Reoko. She then tells him there's more he should know, and leads him to the "Kazuki library."