If "ivvar" is a character from a specific anime or game that Rika has voiced, that might be the link. Let me look up Rika Nishimura's notable roles again. She's voiced Aka in "Majin Tantei Nōnanochi", Hana in "Princess Principal", and others. Does any of those include a character named Ivar or similar? Not that I can find. Maybe the user is mixing up names. Alternatively, "ivvar" could be a username or handle. Sometimes people have friends or fan-made pages with such names, but that's speculative.