Ruin and Rising: The Grisha Trilogy, Book 3

It has Russian names, but Ruin and Rising has no details of the alternate Russian history; the world was established in the first two books. This volume does include some spiritual elements. 

Alina Starkov continues to be a positive role model in Ruin and Rising. She's strong, gutsy, and has a take-no-prisoners mentality. Even though she'll do anything to protect her friends, she still doesn't want harm to come to her people. She wants to be good and help others. Alina's determined to defeat the Darkling, despite having feelings for him. But sometimes she can't trust those feelings because she knows she's being controlled by his power. Mal also continues to be heroic -- a true fighter and leader who loves Alina and wants to protect her. Even though the Darkling has negative qualities and is the villain, we come to know him as a person. There are other characters who are upstanding people and aid Alina and Mal in their quest to protect Ravka and take out evil once and for all. 

There's kissing, flirting, and a brief sex scene. The kissing is more described than the sex scene is, which is more about the heat and passion of the moment than the act itself.