Skin
Their skin held the secrets of their past, had their secrets mapped out across it. Scars told of battles and wars, victories and losses. Tattoos told of commitments and obligations, or loves lost and gained.
Most had entered this life pure, untouched by the trials of their parents, some gained their first marks by the time they were hours old. By the age of five tiny scars told of children discovering that the world is harsh. Age ten carried more lasting marks, showing the fruits of training. At fifteen many had deep scars, badges of battles fought, won, and lost.
By the time they were twenty they had been through war. Some had injures that time would never heal. Others had tattoos showing allegiance to clans, organisations, and duty. Their skin was slowly filling up. It was beginning to tell the stories of their lives.
When they died their skin was covered. They could have told you which each mark meant, why they gained it, who it was for. They could list the ones they regretted, and the ones they cherished.
But mostly the marks were their stories, engraved in their skin.