Mementos Period: By pouring enough love into the repair and crafting of an object, a sentimentalist can turn it into a memento. Mementos work more effectively, more responsively, and more personally than most objects. There are wardrobes that provide clothes their owners have never seen, and pantries that stay as full as you want. Ordinary things can break, or malfunction. Mementos do not.

Antiquarian Period: The state of the art evolves, until eventually, some sentimentalists specialize as antiquarians (as they call themselves). They start creating artifacts- objects which contain the 'personality' of a culture or time period. Where mementos hold personal memories, antiques hold historical memories. Antiquarians amass social power; though only .5 percent of the population, antiquarians controlled about 15 percent of their society's wealth and become renowned as visionaries.

Trophyhunters Period: A few generations later, however, society began to face incursions of monsters which feed on memories. Trophyhunters, another specialized subset of sentimentalists, cropped up to find, hunt, kill monsters. The monsters' remains are often themselves used to construct hunting trophies through kintsugi.
Around the same time, sentimentalists invent memory palaces.

Xenoformer Period: Finally, one day, society faces a type of monster it cannot simply destroy. A man attempting to grow beautiful gardens to complete a commission transforms, to the horror of onlookers, into a new kind of monster; rather than stealing memories, it reshapes the land around it into something unreal and unnatural.