The Dilettante

Stay until you're drunk on me. One day, top counterterrorism agent Hana Lee receives news of her twin brother's passing. Unable to accept the death of her only living relative, she sets out to uncover the truth. Along the way, she gets tangled up with the mysterious Eunseong Yoo and the cold-blooded mafia boss, Giulio Parenti.

Note: The English webtoon was released as R15, it's not R19 like the original novel. It is not confirmed if the Korean release will have a mature (R19) version. This series is the sequel to 페어 트레이드 (Fair Trade) which does not have a webtoon adaptation. The 2nd ML in this story is the ML in The Dilettante