Saeko's Little Sister is a Private Eye A Passionate Lady's Big Secret (Part One) - S1.E41

A new private investigation agency opens next door and it is run by Reika Nogami, Saeko Nogami's younger sister. While Ryo makes constant advances towards her, he learns about Reika's blackmail tactics against Yakuza gangsters as well as the death of her former partner. He also learns that someone has ordered a hit on Reika herself.