If I bought an original work from an artist can I copyright it since the original work and character now belongs to me?

First off, you can’t copyright it because it’s already copyrighted. Under modern law, copyright exists the moment a work is set down in a permanent form. It is possible for the owner of the copyright to then register that copyright, but that is not what creates the copyright.

Copyright in Vietnam 

Second, buying a physical version of a work does not give you the copyright. It doesn’t matter whether that version is the original, or even if it’s the only version. You still don’t get the copyright. The only way you can get the copyright is to buy the copyright. In order to transfer the copyright to you, the owner must do so explicitly in writing, and it must be signed. The only thing you get by buying a physical version of a work is that particular physical version.

Source: Quora