Arrival (Division 5, Book One)
Currently a 5 star ★★★★★ rating on Amazon and Goodreads.

Finding the cure to Cosmos Plague wasn't what he expected it to be.
Arch Extent has been searching for a cure to Cosmos Plague for years. He travels to a dangerous and restricted planet known as Division 5 in an attempt to find an answer.
Winter, a skilled huntress with an icy mutation, has been searching for a place to belong. When the contract of a lifetime is offered to her, she takes it without hesitation. Her contract brings her to a hidden facility where she is exposed to Cosmos Plague, and a man who quickly discovers she is immune to the very thing wiping out humanity on Earth.
Arch Extent becomes obsessed, fascinated by her biology, and is willing to do anything to unlock the secrets of how Winter is immune. Arch Extent makes a deal with Winter, and she becomes his bodyguard as they traverse across Division 5.
The thing is...Arch Extent isn't the only one searching for a test subject like Winter.
Convergence (Division 5, Book Two)

Not all cures are the same.
After the inevitable destruction of Hightop Labs, Winter finds herself awake in the heart of Seraphic on Earth. Panicked at being separated from Reuban, she searches relentlessly for the man at the cost of meeting the monster who would become their biggest threat: Atlas.
Reuban and Winter escape to Division 5 once Reuban's long hidden mutation is revealed. With Winter out of Seraphic's grasp, they reach the one place that holds the beginnings of Cosmos Plague. However, that won't save them from Seraphic's pursuit in recapturing Winter. The two must find allies in unlikely places, as the fate of Division 5 hangs in the balance.
Little does Reuban and Winter know they created something far more inhuman than they could have imagined.
After the inevitable destruction of Hightop Labs, Winter finds herself awake in the heart of Seraphic on Earth. Panicked at being separated from Reuban, she searches relentlessly for the man at the cost of meeting the monster who would become their biggest threat: Atlas.
Reuban and Winter escape to Division 5 once Reuban's long hidden mutation is revealed. With Winter out of Seraphic's grasp, they reach the one place that holds the beginnings of Cosmos Plague. However, that won't save them from Seraphic's pursuit in recapturing Winter. The two must find allies in unlikely places, as the fate of Division 5 hangs in the balance.
Little does Reuban and Winter know they created something far more inhuman than they could have imagined.