Tantei monogatari Bande son (1983) BO

Naomi is a university student who is leaving for the US to study in a week; Shuichi is a washed-up gumshoe who's hired by Naomi's father to bodygard his daughter until she leaves. Shuichi finds the job annoying and wants to quit. But he also has a screwed-up ex and alimony to pay. Things go from bad to worse when Naomi and Shuichi stumble upon a murder which might involve the yakuza. They decide to find out who committed the murder but God knows what it will lead to.