Megami and Fun Girl Theory

Is It True? Part 1

When Megami was young she had an older sister named Fumiko Saikou
Her father loves inventing things He invented a invention that he tested on animals but never saw it on human. So he tried it to his daughter Fumiko and the result was not was his going for. The result was Fun Girl when Megami grew older she realises something was wrong. She forgot and never see her sister ever again after she become Fun Girl.