Yami no Kaze

(from ebookjapan):
Despite being twins, Takamaru and Washimaru have led completely different lives. After his brother's death, Washimaru's destiny was about to change drastically! Takamaru, a young lord of Shirataki Castle, was assassinated. His twin brother Washimaru, whose existence had been kept a secret, happened to be present at the scene of his death. Washimaru is caught up in the family turmoil and goes to Edo to take his brother's place! A black shadow is targeting Washimaru. ...... This is a large scale authentic historical drama that was published in "Weekly Shōnen Sunday" and attracted a lot of attention.