Watashi ga Doushitemo Koroshite Hoshii 5-nin no Papa

A 30-year-old part-time worker spots a prostitute who looks exactly like his first crush from middle school. Determined not to ruin those memories, he keeps his distance, content to just watch her night after night. But when a certain incident pushes him over the edge, he finally decides to approach her. Before he can hand over the cash, however, she gives him a "condition" he never saw coming.

(Source: Shinchosa, translated)