What is a single word for something that takes on shape slowly?

crystallize

to assume definite or concrete form

http://www.dictionary.com/browse/crystallize

For years, I wondered who had signed up for all of the slots, and eventually a character started to crystallize in my imagination.

(from Real Thrills And High Art In A Poignant Page-Turner Of A Novel by Susan Cheever)

There may be an even better word for it, only it seems to escape me just now.

The first option that came to mind for me was coalesce:

1: to grow together

2a : to unite into a whole : fuse

3: to arise from the combination of distinct elements

Emerge (MWD)

1. to become manifest: become known new problems emerged
2. to rise from or as if from an enveloping fluid : come out into view a diver emerging from the water
3. to rise from an obscure or inferior position or condition someone must emerge as a leader
4. to come into being through evolution

"resolve", opposite of "dissolve". "the outlines of his true character resolved only gradually..."