Emperor Blood - Tales of Tenshi, #1

The Vampire Emperor of Menedek is tricked into feeding on a human woman. He loses his throne but rises to lead the Menedek forces against invading humans who want the planets' precious lito. Removed as a threat to the new Empress, Tenshi travels to a human outpost where he joins the trading vessel captained by his brother and human partner. Tenshi meets the human Ann and they become friends. Tenshi is kidnapped from the ship by the March humans he defeated in the war.
The March gloat but all is not what it seems.