(A tale from long ago speaks of Mothra's twin. She was named "Maligno", and the tale spoke of how malevolent she was, unlike the other Divine Moths. Mothra had to step in to stop her twin sister, and eventually destroyed her. However, for unknown reasons she seems to have returned. Sometimes as an astral being, and others as a physical being. These happen within space of all places. So, you decide to investigate it...)

You can start out as a human in a spacecraft, or a Kaiju or whatever

You travel between the Moon and Earth. Flying through space, before suddenly gaining a signal of sorts. An astral creature fades into your vision, before transitioning into a physical being. This is none other Maligna or as others may call her "Gigamoth"

"Yes. It is I~ Mothra's evil twin sister~ I have returned from the brink of death to claim my revenge on her~"