Tokyo Fist

• 1995 Japanese drama: A businessman, Tsuda, runs into a childhood friend, Tajuki, on the subway. Tajuki is working as a semiprofessional boxer. Tsuda soon begins to suspect that Tajuki might be having an affair with his fiance Hizuru. After an altercation, Tsuda begins training rigorously himself, leading to an extremely bloody, violent confrontation.
• IMDb.com link