Shadow and Shadow

This game that takes place in Japan in the year 1640. The main character is a samurai that got a sword with a blade with two shadows (one with a human shadow and another one from the world of darkness) that connect with him with the world of darkness.

The game begins when the samurai travels to a strange island in which all the children are born twins, he hopes that in that island he can find a cure to his own curse. The adventure starts there, can he come back alive from the island and without his cure?