Maou is everything. 

Techniques are strength.

Evolution is power.

Chisson has none of these. He has done everything he's supposed to, but his maou simply doesn't work - and it doesn't seem like it ever will. 

When a stranger appears and offers him a solution, circumstances push Chisson to take the ridiculous offer, leading him down a path to decide the direction of a world where maou itself is transforming.

Chisson must evolve to keep up with it. Change is the only possible way forward.