The basis of this story is taking the concept of evilsekai and push it to its logical extreme.
A quarter of the world is already lost to the Lich Queen, who threatens to destroy all that is alive.
A young physics student wakes up in the middle of the night to realize that she is not who she used to be.
Her memories are mingeld with ones that couldn't exist, memories about magic and a life that is not hers.
Wanting to know what is going on, she sets of to find out what is going on.