The Enchanted Sword Masamune - Break the Soul Possession: A Heart Sings in the Rain?

Tsubaki and Black Star are assigned the task of collecting the soul of Masamune, a demon blade who can possibly become a demon god. After arriving at the village where Masamune was last seen, Black Star is ostracized by its inhabitants, and later he explains to Tsubaki that it was because he is a survivor of the murderous Star Clan, which were destroyed by Shibusen after they started to collect human souls. The duo returns to the village after Masamune possesses the body of a young boy to confront him. Black Star manages to break the boy free from the sword's control and Tsubaki sends her spirit into the demon blade to confront the soul of Masamune, who is in fact her older brother.