The Strength card symbolizes courage in the face of something that looks bigger and stronger than us. It's the inner power that conquers fear, it's self-discipline and perseverance. The Six of Cups is the card of past, nostalgia, reunions. It is considered as one of the 'karmic' cards in Tarot, as some say that it shows connections from past lives. The combination of the Strength and the Six of Cups points to attachment to situations or people from the past.
To understand the elemental relationships between the cards, we should always take into account their actual meaning. The elements of the cards are Fire (Strength) and Water (Six of Cups). This combination shows a battle between the two elements, as Fire and Water are enemies. That's why with this combination, we should expect fluctuations between two different polarities, but in most cases, the influence of the Strength, as a major arcana card, will be dominating.