A/N: People write about Tonks having some "base form", but based on the depiction of Teddy Lupin, I posit that there is no such thing.
Our favorite metamorphmagus will have her own chapter in Connections, by the way (year 7, I think). This is just a bit of a character study in preparation.
About pairing: I left the POV vague. Pick a male character (except Dumbledore, because he's gay, or Snape, because he's all angsty about Lily) and go with it. Even Hagrid. Or Dobby. Or Griphook.
He watches her when she sleeps. As a metamorphmagus, she's in a constant state of flux. Her hair color cycles through the rainbow, her face rearranges itself. As her eyes flick from side to side, he can imagine their irises shifting from color to color.
She's chaos personified, and he loves it when she lets go at night. During the day she's static, her hair remains the same bubblegum pink, her face the same heart shape. She has to force her physical form to remain constant during the day.
He knows she'll move on. She embodies change, and the only certainty about their relationship is that it won't last. But at night, he can imagine seeing her shifting form years into the future, and despite knowing that this future will never pass, despite knowing that this hope will cause him nothing but pain, he dreams.