Patriotism (Second Edition) (New Directions Pearls) 2nd (second) Edition by Mishima, Yukio published by New Directions (2010) -

The Sino-Japanese tradition was very important to Yukio Mishima (January 14, 1925 – November 25, 1970), who held strong ideals of the militaristic glory days of old Japan. 

In Patriotism(1960), Mishima uses the love-death theme executing the ancient ritual suicide, viscerally playing it out through a recently married couple. Lieutenant Takeyama returns home following the failed coup d'état of 1936, the Ni NI Roku Incident. Rather than following orders to execute the rebels- his friends, the young army officer decides to commit suicide- his farewell note would read: "Long Live the Imperial Forces--," revealing his own true ideology. 

The story unfolds in a timeframe of a few hours, in an unsettling and evocative mix of contrasting effects, of sexual and gruesomely graphic scenes, as Mishima manages skillfully and poetically to balance sensuality with darkness.

The lieutenant drew his wife close and kissed her vehemently. As their tongues explored each other's mouths, reaching out into the smooth, moist interior, they felt as if the still- unknown agonies of death had tempered their senses to the keenness of red-hot steel. The agonies they could not yet feel, the distant pains of death, had refined their awareness of pleasure.....

At the touch of his wife's tears on his stomach the lieutenant felt ready to endure with courage the cruelest agonies of his suicide.

Takeyama considers his final act with the courage of a soldier entering battle, to "a death of no less degree and quality than death in the front line." For Reiko who, almost in a dreamlike state, would bravely follow him, honoring their death pact like the dutiful spouse: "The day which, for a soldier's wife, had to come, has come." 
The last moments of this heroic and dedicated couple were such to make the gods weep. 

Mishima's obsession with death was bewildering from a young age, if not plainly disturbing. Death themes frequently appeared even in his earliest works. In Patriotism, the melding of self-annihilation and erotic pleasure is expressed with deep feeling: it is absolutely apparent to this reader that the story was a rehearsal for the plan he had in mind as his own final act on November 25th, 1970. 
See Mishima: A Biography
and wiki on Mishima

In the movie adaptation, Yūkoku- the Rite of Life and Death, Mishima dramatically (over)played the lead with considered intensity and vigor - his emotional investment in the act of the ritual itself seemed so well-thought out, and so very personal.

My copy of Patriotism is from Death in Midsummer and Other Stories, an extremely worthy collection showcasing Mishima's mastery of the short story form.