Gemini and Aquarius share the air element: you meet in ideas. Conversation never runs out — plans, theories, inside jokes. The risk is living in your heads: this bond does well to ground things and say what's felt, not just what's thought.
One holds steady (fixed), the other flows (mutable): the fixed one gives the mutable roots, and the mutable teaches the fixed that changing isn't losing. Complementary — as long as neither caricatures the other as 'stubborn' or 'flaky'.