I Thought About You 2: Beasts That Are Too Kind (2002)

Years have passed since the first film. Goro never got over the death of his partner and continues to drown his misery in alcohol. His latest work as a private detective involves spying on a man suspected of adultery by his wife. She happens to be right, but he's cheating on her with a male university student and not another woman. When that student turns up dead shortly after Goro delivers his results, he is initially indifferent. But then he's absudcted and beaten to within an inch of his life by people who clearly want to ensure his silence, and that changes things. Turns out, his past once again comes back to haunt him.