Be sure to check out my review of Hiroshi Sakurazaka’s military science fiction novel ALL YOU NEED IS KILL. From the review:

ALL YOU NEED IS KILL is the story of green recruit Keiji Kiriya fighting an epic battle against aliens called the Gitai determined to terraform Earth for themselves, even if that means turning it into a wasteland for its current inhabitants. To save the planet, Keiji must figure out the secrets of the Mimics, but first he encounters the legendary Full Metal Bitch — a woman with a crimson mecha “Jacket” named Rita Vrataski. Humans have outfitted themselves with “Jackets,” mecha suits equipped with numerous weapons onboard, none of which have much impact on the aliens. Nicknamed “Mimics” because they mimic the appearance of the first creature they came in contact with — starfish — the Gitai stand about four feet tall, possess multiple limbs, a hard exoskeleton, and shoot razor-sharp “javelins” from their bodies in battle.

Only one soldier has made a difference against the Mimics, taking out about half of all the Mimic kills humans have made overall. They call her the Angel of Death, Valkyrie Incarnate, or Mad Wargarita and the “two-metre-long behemoth” of a battle axe she’s attached to her Jacket instead of a regulation pile driver makes all the difference. Stuck in an unexplainable time-loop, Keiji gives in to his fate and decides to become a warrior to rival Rita. After all, he has all the time in the world. On his 158th iteration, Keiji receives a message from Rita with the key to his escape and the secret of defeating the Mimics.