Warhammer 40K: The Weeping One’s Penitent Crusade

A different kind of Mourner, a different kind of Crusade. When the protagonist takes them back to an earlier timeline and they appear in every major battle, a different journey of atonement begins.

The protagonist is wearing someone else's body. He can come back to life, but it hurts.

The synopsis isn't doing it justice, so go read the story.

My writing is limited, so please bear with me.