Sein

Sein is an essential part of The Brightest Shadow, the world's equivalent of qi. Different cultures approach it in different ways and thus produce very different results but all begin with gaining awareness of sein through the five senses. Each sense is different for each person, so one person might smell mint while another smells alcohol. A person's quantity of sein can be increased through training, but gaining a deeper understanding of it via a new sense is a more important way to improve.

The scale of sein power was described like this in this thread:

"Warriors on the lowest hill can do things at the peak of real human achievement. Those on the second (where the main characters start) can lift boulders, leap great distances, or cut through metal. Experts can do all of the above, plus their personal strengths make them nearly unstoppable to lesser warriors. The peak of mastery is intentionally steep and tall, but masters can face down armies."

The varying paths were described like this:

"Sein itself isn't linear either. In addition to being unique to each person, there are many possible paths toward mastery. A person who sees and hears sein will be different from one who feels and smells it, for example. This is actually more complex than the characters in the first book's setting know, so I intend to unveil the whole system as is natural for the story."