I will use "slutty" in this sense: "sexually assertive" or "not innocent/naive" or "flirty and experienced" ... NOT necessarily in the "sexually promiscuous" sense.
I've only found such Female Leads in older lakorns. Lakorns (especially older ones) have some of the best FLs in Asian dramaland: Independent, assertive, smart, clever, tough , outspoken .... Not the usual 1-dimensional kick-a** types, these women have flaws and vulnerabilities. They can be "slutty", alcoholics, bitchy, gold-diggers dating 3 men at a time (2 are father and son - she's my fave, lol) , etc...
I must warn about lakorns, there are culturally specific beliefs and behaviors, which may offend most viewers. Although, they tend to be low in quality, they have well-developed characters , smart insightful writing, and intense romance. ... Most of my ratings of lakorns are average or below, but my enjoyment of them is above average. They are a guilty pleasure.
Generally, Anne Thongprasom , plays strong, independent, smart female leads, sometimes vulnerable, other times kick-a** tough.
There are many I could list, here's a couple to start:
Samee Teetra (2001) --- She's an alcoholic, previously married 3 times, and is now pursuing a shy, reserved gentleman. She makes all the first moves, she asks him out, she initiates the first kiss, she even asks him to marry her.... he is confident and manly enough to handle it ;)
Luk Mai Klai Ton (2000)--- She's smart, mature, insightful, assertive, outspoken and understanding. She's honest and not afraid of her feelings, confesses her love first while telling him that they could never be, "...because I love you, and I'm not trying to stop my heart either, although I should." ... . The story is about "Love vs. Responsibility" a mature honest love development b/w two personalities who are perfectly complement one another.
Also, some supporting female characters in J-dramas can be labeled "slutty" as in cheating or sleeping around. Some FLs have affairs or one night stands, usually in older J-doramas.