Firstly, HUGE shoutout to @shmoop for making the cover for me!!
Ok, lets assume this is a game with a similar mechanic to Kirby Super Star.
-You are in space and you accidentally discover an abnormality. You head towards it out of curiosity. You are now exploring the edge of the astral realm. Here, there are both properties of space and the astral realm, which is why things would seem abnormal. Unfortunately, you, unknowingly, aren't supposed to be there and now you are under attack. The entities that are attacking you do not want you to leave, and want to kill you instead. Your goal is to escape.
PS: I am not a writer, so this story is probably bad or bland, but I just wanted to give some kind of explanation here.