In the world of BBK/BRNK, It’s been ten years since Azuma Kazuki has been in Japan, and upon his arrival he is taken prisoner by a group of armed men. Azuma is saved by his childhood friend, Kogane Asabuki, thanks to a living weapon she wields on her right hand, known as a Bubuki. Learning about these weapons, Azuma becomes a Bubuki wielder himself and sets out on a journey.

[Source: Crunchyroll]

When Azuma Ikki returns to Japan after 10 years, he gets assaulted by a group of armed men and becomes their prisoner. Kogane Asabuki, a childhood friend, saves him with a weapon on her right hand known as Bubuki; a weapon with its own mind. Azuma Ikki, who is a Bubuki user himself, learns about the existence of Bubuki and goes on a journey alongside the companions he has found, in an attempt to find and revive Oumai, a Buranki (titan) who sleeps underground.

[Source: MyAnimeList News]