Reunion after Twenty Years: Please look after my Sister, Mr. Saeba (Part 1)

A woman named Sayuri Tachiki approaches Saeko with a request to meet her long lost sister, who happens to be Kaori. Because Kaori does not know the truth of her existence, Ryo decides to take Sayuri on as a "client" and have Kaori interact with her to see what happens. Ryo then notices that someone may be after Sayuri.

Synopsis excerpt via Kitsu.