Dark Heavens

Dark Heavens is a trilogy of novels by Kylie Chan (White Tiger, Red Phoenix, and Blue Dragon). It has a sequel, the Journey to Wudang trilogy of Earth to Hell, Hell to Heaven and Heaven to Wudang. A further trilogy is upcoming.

When 28-year-old Emma Donahoe becomes a nanny to John Chen’s daughter, Simone, she does not expect to be drawn into a world of martial arts, magic, and extreme danger, where both gods and demons can exist in the mortal world.

Emma gradually realises that John Chen is no ordinary businessman and that nearly all the demons in hell would like to see him dead. John and his American bodyguard, Leo, begin to teach Emma their particular brand of martial arts and special defensive techniques … they also begin to realise that there is something that is different about Emma but exactly what it is, nobody can say.

Tropes used in Dark Heavens include:

Action Girl - Emma Donahoe, after she starts learning martial arts. Also, Lady Win Chun, though she never actually makes an appearance, is implied to be this.
Exclusively Evil - Demons, though if they repent, they can swear loyalty to an Immortal... in the eventual hope of attaining perfection in a few hundred years and becoming human.
Awesome but Impractical - Emma is able to generate an ultra-rare black chi, which can instantly annihilate demons, or turn them human... sometimes. Other times, it does nothing at all. Eventually, Emma decides it's too unreliable and stops using it... for now.
Author Avatar - Emma Donahoe's nationality and appearance bear remarkable similarities to the author's.
Biological Mashup - The Xuan Wu. Not at the moment though. And the children of Gold and Amy should be interesting.
Break the Cutie - Simone.
Brick Joke - Consider the twist at the end of Heaven to Wudang. And then go back to the very first line of the entire series.
Buffy-Speak - "Demon stuff".
Can't Have Sex Ever - Certainly puts Twilight in perspective. Although they get around it a few times.
Cannot Spit It Out - John and Leo towards Emma in the first book. Regarding pretty much everything.
Celestial Bureaucracy - The series is based on a mish-mash of Buddhism, Taoism and Confucianism.
Dark Is Not Evil - Hard. One of Xuan Wu's official titles is "Emperor of the Dark Northern Heavens", or just "The Dark Lord" for short.
Defeat Equals Explosion - Demons.
Even Evil Has Standards - Even other demons are surprised at Simon Wong's complete lack of anything resembling honour or morals.
Everyone Calls Him "Barkeep" - Kwan Yin, a Bhoddisatva, is normally referred to as "Mercy", this being her divine role.
Half-Human Hybrid - Emma, Rhonda. Much to the latter's misfortune. Simone and Michael also qualify (Half-Shen). In Michael's words; "And I really am half goddamn Tiger!"
The Four Gods - Chinese version, including the fifth, Huang Long.
Really 700 Years Old - a large part of the cast are Taoist Immortals, with John Chen himself being over four thousand (Emma comments once that The Golden Boy, a mere 500-something stone, is 'far too young for her')
I Just Want to Be Normal - Simone in the fourth and most of the fifth books.
Jerkass Facade - Qing Long.
Limited Wardrobe - Mr. Chen wears black. All the time.
Love Triangle - Subverted and averted. Emma believes Jade's dislike of her to be jealousy over Mr. Chen. Actually, Jade just thinks she's a gold-digging bitch. Also, The Tiger really, really wants Emma to be Wife #102.
- Leo has long been in love with John, but was good friends with John's first wife Michelle, and now Emma. He then starts a relationship with John's son Martin, while still in love with John.
Magnificent Bastard - The Demon King. Granted, it's probably in the job description. The climax of Heaven to Wudang drives the point home.
The Masquerade - Subverted. Pretty much everyone has heard of Pak Tai, God of the Water... they just don't expect him to own a high-rise in Happy Valley.
Mayfly-December Romance - Pretty much any human/Shen relationship. Notably Emma/John, Rhonda/Bai Hu, and Gold/Amy.
Mighty Whitey - A young, white Australian nanny with no previous training goes to Hong Kong, develops superhuman martial-arts skills and magic qi powers in just a couple of years (certainly by the end of the first book in the first trilogy), beats up demons and generally proves herself the equal of Chinese gods, never mind mere mortals.
- One post on the forums also wondered about Rhonda and Michelle, both white women who attracted the attention of male Shen, and asked the question, what is so special about these three seemingly normal white women?
New Powers as the Plot Demands
Red Baron - Leo is known as "the Black Lion".
Reptiles Are Abhorrent - Discussed at length. Also serves as a Berserk Button for John.
Scary Black Man - Leo.
Shout-Out/Memetic Mutation - The first time Emma transforms into a snake, she's Snakes on a Plane on a plane. Leo, of course, is there to point out that she's a motherfucking snake. John later complains of a similar joke regarding his serpent half.
- There are also frequent Shout Outs to geek favourites such as Good Omens, Discworld, Doctor Who and others. Kylie Chan is obviously One of Us.
Staying Alive - Lampshaded when an official in the courts of Hell complains about Emma's Retainers constantly getting killed.
Supernatural Martial Arts - Of course.
Took a Level in Badass - Emma takes several levels over the course of the series.
Translator Microbes - One of the benefits of living in the Chen household.
Twofer Token Minority - Leo. Black, gay, and human. The last one ceases to be a problem following the end of Earth to Hell. Also, HIV-positive, and later paraplegic.
Why Did It Have to Be Snakes? - Leo really doesn't like them. And look who he ended up working for. And also water.
Xanatos Gambit - Oh God.