Border Series by Kazuma Kodaka

Yamato is man with a darkly dramatic past. Perhaps it is no surprise that he now runs his own detective agency. With a staff of three misfits that are practically family to him, he does whatever it takes to get the job done. Unconventional cases can mean unconventional solutions, but Yamato is not one to shy away, except when his heart is concerned. The creator of Kizuna brings a story of mystery and romance.

The target for Yamato and the guys is the truly evil Zama, a sleazy drug dealer who forces runaways and kids under his control to push for him. But Zama’s also the man who left a teen-aged Tamaki deeply scarred. Though he knows all too well how demented Zama can be, Tamaki insists he can stop the monster dead in his tracks! Will the team race to his aid when he needs them most?