宿怨
an old grudge; old scores to settle
宿缘
(Buddhism) predestined relationship
泝源
variant of 溯源[su4 yuan2]
溯源
to investigate the origin of sth; to trace a river upstream back to its source
诉冤
to complain; to vent one's grievances
诉愿
to appeal; an appeal (law)
夙愿以偿
a long-cherished ambition is realized
夙愿得偿
to have a long-cherished wish realized