Capcom’s announced the return of Onimusha, but not in the way you’d like. The series will return as a Japanese browser-based social game called Onimusha Soul. Soul will be a Sengoku-era strategy RPG that will feature characters from past games in the series, with players controlling of a feudal lord in a region currently at war.
The last big Onimusha console title was Onimusha: Dawn of Dreams in 2006. More details are on Andriasang.