The skill itself won't change level, but it's applied effects will increase.

Let's add more descriptive info to the skill description to avoid confusion.

Thanks Masamune! Rush is meant to stay at level 1 for Dawn Warriors: it grows with your weapon Mastery instead. At Mastery 7, 14 and 20 the charge reaches farther and shoves more monsters, and with Mastery 20 you're already at its strongest. The skill's description now spells out each step so it's clear.