I wrote this in a quarter of an hour in the middle of the night because I couldn't sleep, so criticism is as much needed as wanted!
She was fire. She destroyed his emotions and his ability to think rationally. She shouted, she screamed, she ranted. Her flame-coloured hair danced as she moved. Her eyes blazed with fury and with anger. Yet she also warmed. She helped the first years to settle in, was willing to help anyone with anything if they needed it and was always ready with a kind word and a smile for anyone except him. She glowed like embers, her radiance coming not only from her outward appearance, but also from her actions and her personality. She was fire, she was Lily.
He was water. Fun and invitingly attractive like a bubbling mountain stream. Cool and calm like a lake. Yet beneath the surface he was tempestuous, filled with feelings so strong he wasn't entirely sure how to cope. He was like the sea, deeper than people expected, though he'd cheerfully admit he was shallow in places. He was an oxymoron: dependable but changeable, dangerous but life-giving, clear but muddy, still but always moving. He was water, he was James.
They were complete opposites, they should not have fitted together so perfectly. But when they had stopped emphasising their differences and took a chance on love, they found that instead of the water extinguishing the fire, or the fire vanishing the water, they simply changed, forming a new element. They became steam, rising together eternally.