I have literally no idea where this idea came from but I decided to run with it. I don't own any rights to Doctor Who. Enjoy!
Fire. The Master was fire.
He could rage through the universe, destroying everything in his path. Everywhere he went, he left a scorching mark. Big or small, he would leave the blemish of his presence. He was a powerful and unstoppable force whose blaze blinded the weak and challenged the strong. He could use anything within his reach to his advantage; to make is power grow. He was not easily kept, controlled, or tamed. The Master was Fire.
But the Doctor was ice.
He could slip through into almost anywhere. He soothed and healed the weak and the ones in need. His soul so clear yet so fragile; one touch in the wrong place and his hearts would simply shatter in two. He was delicate yet strong. His mere presence radiated cherishing and love. He would care for anyone. Something as simple as his touch could heal the hearts of broken men. Yet when those he loved and protected were threatened, he became a harsh, crushing weapon that would destroy anyone in his way at the flick of a hand. The Doctor was Ice.
Fire melts ice when it gets too cold. The Master gives the Doctor the warmth and love he needs when is soul begins to freeze. Ice cools fire when in burns too bright. The Doctor calms the Master when the drums become too loud to bear.
The Master and The Doctor; Fire and Ice.