intense, large
祁 centers on something of great scale or force: large in size or intense in degree. The two meanings are closely related, with 'intense' being a natural extension of 'large' applied to qualities or feelings.
祁 combines 示 (altar, spirit) with ⻏ (city, place), but the exact historical development is uncertain. It may have originally referred to a place name or a concept of greatness associated with a location.
Imagine a massive altar (示) next to a towering city wall (⻏). The scale of the altar and the city together conveys something large and intense.
For キ, picture a giant key (キ) unlocking an enormous, intense force. The key's size matches the kanji's meaning of 'large' and 'intense'.