The real kaname is shown in the mirror in chaptor 52 in the manga- and yes that was the ancestor kaname both times. He became darker because of What happened to his parents and yuki and he was looking for revenge. He was nicer before because he was happy..
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Tenken's Smile
I can't remember which chapter revealed it, but it was early on in the manga series...Japan and china are 4/5 manga vol. ahead of us, so you might not of reached it yet...
