The World is the final card of the Major Arcana, that's why it's associated with completion and endings. It's also associated with journeys and traveling. The King of Cups foretells that emotions, relationships, matters of the heart will be in the foreground. If not ill-dignified, the King of Cups indicates that we have the experience and the maturity to deal with emotional matters efficiently. In his negative manifestation, the King of Cups can become, cold, manipulative, cruel. The combination of the World and the King of Cups signifies completion and fulfillment.
To understand the elemental relationships between the cards, we should always take into account their actual meaning. The elements of the cards are Earth (World) and Water (King of Cups). Earth and Water blend well and strengthen each other, creating a stable and secure environment. There are no surprises here and everything goes according to plan. This combination can at times manifest as delays, since both elements are passive and slow, but the World and the King of Cups combination gives the promise of a positive outcome.