Soul Sacrifice, as Keiji Inafune explained to Siliconera, is designed primarily as a multiplayer game since players can sacrifice themselves for the good of the group. If you’re flying solo, Soul Sacrifice gives players a partner character, like Nyume.
Nyume is a beautiful sorcerer who the hero meets in the story. All AI partner characters learn from the player and change their tactics based on the player’s decision. There are more possible party members, but right now Famitsu only announced Nyume.
Soul Sacrifice revolves around the concept of sacrificing organs to cast powerful spells, but you can also use items as offerings. Sacrifice a giant bone and you can make a bone fist and crush enemies.
Players can also "sacrifice" stones to make a wall that defends against magic.
Soul Sacrifice is slated for release this winter in Japan.