Kurata Yasuaki made quite a good living in Hong Kong, playing one Japanese bad-guy after another. He even played a Chinese bad-guy on occasion, as in Prodigal Boxer (the Meng Fe film). The only time in the '70s when I can remember him playing a good-guy was in a Japanese film, the Sue Shiomi film Dragon Princess.
As any one should know, who has seen the Jet Li remake of Bruce Lee's Chinese Connection, Fist of Legend (wherein Kurata plays an aging karate master), Kurata's acting ability is really quite broad and quite strong. that he got himself lost in Hong Kong type-cast as a villain is therefore a little disheartening.
At any rate, his performance in this film is really top-notch; and despite his being Japanese - and a spy - and despite his confrontation with the hero at the end, he actually plays a decent guy! His character - marvelously complex for this genre - someone we find easy to like - so that when the bad things start to happen, we feel as upset and confused as the young hero.
This is not one of those all-good or all-evil morality plays we often see in old-school chop-socky films. although this film technically still belongs to that tradition, the audience - as with the hero himself - is caught in a terrible grey zone where one must destroy those one loves, for the sake of a better future for all; and where one's heroes can prove nastier than one's enemies.
I should also remark that this appears to me to a quasi-autobiographical film for director Yuen Woo Ping - This isn't so far-fetched - the Yuen family is among the most respected for having produced martial arts instructors and Chinese opera performers -arts that involve considerable - and frequently harsh - disciplinary training.
At any rate, whatever the source, the writing of the film makes this one of the strongest of its genre and of its period.