Remix: Daring-doo and Sadness (The Shade's Remix) [Ten, Astrid, 100 words, rated PG, character death], by aralias
Some companions force themselves on him - he only learns to love them later; others he tests before allowing onboard. But there are some he has always known without knowing: it’s just a matter of their time-lines intersecting at last. Astrid Peth is one of these. The Doctor knows immediately that she is his. He takes his beautiful new Astrid to an alien planet, knowing it is the first of many.
But then she falls.
Grieving for more than a passing acquaintance, the Doctor turns Astrid to stardust. Only the sight of his beautiful old TARDIS consoles him after that.