Skyscrapers of Oz (2001)

Blurb:
Mari Kudoh and his partner Yoichi are drop-dead gorgeous "Handymen", as they prefer to call themselves. With a dangerous "back-door" operation, these two lead a double life as seductive hitmen! Their latest assignment is from the vengeful wife of a prominant CEO. She’s determined to humiliate her aging husband’s paramour, a handsome young man named Yu Kaito. But before Mari can begin this mission, he finds himself rescuing the intended target from a vicious street attack...and then sheltering him in his own apartment.

Source: www.anisearch.com/manga/1600