Campbell award winner Wesley Chu's The Lives of Tao series is on sale today for $2.99 in advance of the release of a new book in the series on Tuesday.
The gist of the series is that the Quasing, a group of aliens crash landed on Earth many millennia ago, they're gaseous entities who can only survive in our atmosphere by getting absorbed in the bodies of animals (including humans), and they can only migrate to new hosts when their current hosts dies. Eventually they discovered humans made the best hosts because they can communicate with their human hosts and we can do things for them. In our time, there are two groups of aliens.
Tao is an alien of the second group, whose host has just been killed, and Roen Tan is a drunk twenty-something in the wrong place at the wrong time. Tao enters Roen and co-opts him in the fight between the alien groups. There's aliens, martial arts, and I enjoyed the series a lot.
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There's also a novella from Subterranean Press that's not on sale, but it's couponable at Kobo. The new release, Rise of Io will be focusing on a new Quasing and human host.