New World Another World War

What if after his death on the western front Manfred von Richthofen was brought to a new world, this world being set where sirens plan on ending humanity and 4 major factions have split in 2 group now fighting each other while sirens continue to progress in slowly killing off humanity. how will the world react to him being alive, how will he bring the all groups together, and most importantly will he survive long enough to accomplish theses goals?

I do not own Azur Lane or any of its characters
I only own the idea of using the history of the Red Baron to make this story possible
first story don't expect much from me but I will try to make a good story and use advice given to me.