The answer is Peter Brett's Painted Man books, thank goodness someone mentioned it less than an hour after I asked. Many thanks!
The novel follows three POV characters in their passage from childhood to maturity. They are inhabitants of a world plagued by the attacks of demons known as Corelings, which rise from the planet's core each night to feast upon humans. There are many different kinds of corelings, each associated with a particular element and each with different capabilities and strengths.
The ongoing attrition of these attacks have reduced humanity from an advanced state of technology to a dark age. The only defense against the corelings are wards (magical runes) that can be drawn, painted, or inscribed to form protective barriers around human settlements. These are, however, fragile and prone to failure unless properly maintained.
As the novel progresses, the protagonists each embark upon his or her own hero's journey in an effort to save humanity.
Arlen is introduced in the aftermath of a coreling attack that claims 27 lives. Those happen often, usually due to marred or misplaced wards. He realizes that humans have been mostly on the defensive, hiding behind wards. During an attack which endangers his family he overcomes his fears of the corelings and attempts to fight them off, though with little success. He is disgusted by his father's cowardice after his mother is attacked, and leaves his home to seek training as a messenger, a traveling warrior-nomad responsible for maintaining trade and communication links between villages. As he matures he becomes determined to hone his skills and help turn the tide against the corelings. In the second half of the story, Arlen discovers the lost combat wards inscribed in the ruins of Anoch Sun. Betrayed by the men of Krasia, he uses the wards on himself, becoming "The Painted Man".
Leesha is a thirteen-year-old girl who lives with her abusive mother and downtrodden father. After a slanderous rumor spread by her fiancé seems to destroy her chances of a respectable marriage and shows the true nature of many of her friends and the hypocrisy of the villagers, she devotes herself to learning the ways of herb gathering to care for the sick.
Rojer enters the narrative as a toddler, the only member of his family to survive a coreling attack. He is rescued and adopted by an alcoholic jongleur, a type of roaming jester that frequently travels with messengers and performs in villages on the messenger's route. Rojer has a crippled hand, caused by the loss of two fingers in the coreling attack that killed his parents. This limits his ability to juggle but does not hinder him in the least when he plays his favorite instrument, the fiddle. He later remembers that the jongleur that adopted him actually caused the death of his mother, he confronts him on the road about this later, and the jongleur, in a fit of drunken rage, pushes him into the corelings. He then sees his mistake, and dies in order to save Rojer's life. With his fiddle Rojer can entrance the corelings with his music causing the corelings to follow him, anger them to rage, make them oblivious to others, or drive them away with jarring music. Rojer tries without success to teach others his skills with the fiddle. Rojer harbors strong unrequited feelings for Leesha.