One of the attractions of Asian martial arts for many Westerners (including this one) is the promise of self-improvement that goes beyond better street fighting.

In Kazuyoshi Kumakiri’s “Mukoku,” a turgid film set in the kendo world, mastery of the sword is supposed to not only focus the mind and elevate the spirit, but also promote love of country and world peace. But these ideals, expressed in the wall hangings that decorate the Kamakura house where an alcoholic security guard (Go Ayano) once lived with his kendo master father (Kaoru Kobayashi), now ring hollow.

The guard, Kengo Yatabe, was a kendo instructor himself, if one who never calmed his turbulent spirit. As we see in flashbacks, his father Shozo was a brutal disciplinarian who taught his son with shouts and blows to instill fighting spirit. Instead, Kengo came to despise his father while regarding kendo’s higher aims with bitter cynicism. (His understanding mother, who served as a father-son buffer zone, is now deceased.)

Enter Toru Hada (Nijiro Murakami), a young rapper who discovers a talent for the sword in the high school kendo club Kengo once coached. He is encouraged by an elderly Buddhist monk (Akira Emoto) who mentors the club while Kengo lolls in an alcoholic stupor with his similarly sozzled girlfriend (Atsuko Maeda). But when an out-of-shape Kengo tangles with a feisty Toru in a sparring match at the dojo, the boy miraculously scores a point — and a fierce rivalry is born.

Based on Shu Fujisawa’s 2012 novel of the same title, the film resembles Showa Era (1926-89) manga that glorified supokon, the fighting spirit of baseball, boxing and other macho sports, as well as classic jidaigeki (period drama) with dueling sword masters (see Kenji Misumi’s 1962 “The Tale of Zatoichi” for one excellent example).

The setting in a modern-day Kamakura of rappers and surfers thus feels oddly anachronistic, as does Kengo’s self-destructive alcoholism, including lengthy imbibing sessions at a bar run by his father’s former mistress (Jun Fubuki).

But Kumakiri, whose work frequently features marginal types and explosive violence (as seen in last year’s “Dias Police: Dirty Yellow Boys”), keeps the focus on his principals to a claustrophobic extent, taking only occasional glimpses of the world beyond the dojo and the Yatabe family home. His aim may be intensity, but the repeated confrontations with bokutō (wooden swords) at every opportunity, start to feel butter-knife dull.

What’s at stake? In a supokon manga, it’s the big game. In “Zatoichi” it’s professional and personal pride for the blind hero. In “Mukoku” it’s not as clear, though it soon becomes obvious Kengo’s real opponent is Shozo, now lying unconscious in a hospital ward, for whom his son feels both hatred and love. Meanwhile, Kengo is battling his conscience — and a death wish.

As Kengo, Ayano bombastically chews the scenery, similar to his over-amped performance as a corrupt cop in last year’s “Twisted Justice.” Co-star Murakami, now 20, more than matches him in on-screen volume, and far outshines him in sheer athleticism, dodging and darting like a true kendo prodigy.

“Mukoku” has the feel of a last hurrah for the supokon genre, but the jidaigeki will never die as long as there is a Japan. And Murakami may be its new voice — rapping optional.