Fire emblem three houses: all 5 unite (doctorwhoX Fire Emblem crossover)

In fodlan the three kingdoms are at war. Byleth was with Dimitri at the field. As Edelgard and Claude came all began to fight until something came from the sky. A army of unknown aliens saying exterminate and unknown aliens and creatures came and killed everyone including Claude and Edelgard. Dimitri sacrifice himself to save byleth. As she escape she then had no hope until a police box came. Out came a woman who is named the doctor. Now the doctor and byleth will have to save fodlan with help from the doctors and companions from the past.