*They were exiled to an island named Kikai-ga-shima, thought to be modern day Iōshima
"The Tale of the Heike, translated by Royall Tyler, 2012
1 (often capitalized) : the force generated by a person's actions held in Hinduism and Buddhism to perpetuate transmigration and in its ethical consequences to determine the nature of the person's next existence.
2: a characteristic emanation, aura, or spirit that infuses or vitalizes someone or something.
(Mirriam Webster Definition)
Although Karma is generally thought of in the ways above, in "The Tale of the Heike" there is another mode of Karma, one that is almost immediate and can negatively or positively affect people. Usually this Karma stems from the death of an individual who felt strongly about something before their death and it was not reconciled during their life. Having angry spirits about stems directly from the bad karma one can acquire throughout ones life.
Karma has a very important role within "The Tale of the Heike." It can be found in nearly every Episode of every Book and helps to bring about massive consequences for the people of Japan on a regular basis.
Within Book 3 there are numerous occasions where Karma is mentioned and its power is felt by all; whether directly or indirectly correlated there is always an action and a reaction that occurs.
This begins with the pardoning of the exiles in Episode 1 and 3, when Kiyomori wants his daughter to have a son he needs to create peace with those in exile and those who have been disgraced by the Heike. This means posthomonously granting a disgraced prince and emperorship, and reinstating a empress with her estates. The pardoning of Naristune and not Shunkan also brought about karma's retribution over time. Kiyomori was selfish and this came back to bite him as the Book goes on.
Shunkan's death during Episode 9 brought bad Karma upon Kiyomori and the Heike that could have easily been avoided. This death caused the immediate reaction of a large whirlwind in Episode 10, which destroyed much of the capital and foretold peril in the realm.
Kiyomori's son Shigemori also attempt to build up good Karma throughout his life so that he will be protected in the afterlife. Kiyomori causes much negative Karma to come to his children though, in Book 3 Episode 5, he is given an oracle by the Triple Goddess defining that if he conducted himself ill, then his descendants would be the receivers of the consequences. Therefore, Shigemori's actions during his life, as well as those done by Munemori, Tomomori, Shigehira, and Koremori, are nullified greatly by their father/grandfather Kiyomori.
Shigemori in specific attempts "in all things.... to abolish sin and cultivate good karma." (Episode 13 Book 3) Thus, he built a temple forty-eight bay long with forty-eight lanterns, in these bays people called to Amida and prayed for enlightenment. This built up good Karma for Shigemori, since he was searching for Budhist enlightenment. In this same vein of thought, Shigemori knows that his descendants couldn't pray for him forever, thus he sent three thousand five hundred taels (50 grams = 1 tael) of gold to China. This money was to be split for several things, five hundred to the sship captain who was to bring it to China, one thousand for the monks of Mount Yuwang, and two thousand for the Chinese emperor so taht he could buy rice paddy fields for those monks. In this way, Shigemori could assure that prayers for his rebirth would continue to go on long past his death.
These mentions of Karma within Book 3 certainly are not all of them, see if you can find any more instances where Karma had an immediate effect upon other characters, whether within this Book or within another.