There’s Monster Girl Haven by myself and Jamie Hawke

https://www.amazon.com//dp/B08HX8ZNGQ

Outnumbered and outgunned, a mercenary's only hope is the lost elixir of life, and the help of three monster girls!

When Greg Hadder's mercenary company is tasked with finding a treasure with the power of immortality, he thinks it's a wild goose chase. That is until his brothers-in-arms are gunned down by a mysterious rival group, and he's left with nothing but his wits and his rifle to survive.

Using maps and ancient artifacts, he must navigate traps and find his way to the center of the exotic island to harness the powers of the gods themselves. When he decides to stand his ground against the soldiers bent on stealing the elixir, he calls upon his new allies - a feisty catgirl, an elegant siren, and a cold-blooded lamia - to help him.

Together, they'll have to fight creatures that haven't been seen for millennia... and save the world!