What is a Doppelganger?

a word that comes from tadesco ( "double-walking") is the embodied soul, the evil twin, your double. a sort of figure that appears before you. It is said that when it appears before our eyes this individual shortly after six finished in the tomb. causes confusion with his evil suggestions double evil and people who are around you

Light Yagami and kira.
are the same person (I follow?)
Light Yagami, however, is a normal student, intelligent and with great ideals of justice.
kira is a ruthless murderess who incites the people (his fans) to believe and tifare for him.
com we have said, the evil Doppelganger advises and malicious people to surround chee ma anke his double (light in this case). then I thought that the Doppelganger of light is precisely the same version if kira, or when it is possessed by the power of the notebook. that is to say that his poor sister lives in his own body and comes out only at certain times.