A young teenager named Michelle (often called "Mei") who is 13 years old wakes up in...ANOTHER UNIVERSE!? 

It all happened by following a feral black cat. She noticed a purple portal and then see's the cat walking into it. She tries to get the cat away from the portal but then, she falls into the portal wakes up in space or she thinks. 
She passes out and wakes up on earth expect, turns out she is in another universe. She meets humans who are different in their universe and finds a way to get home.