Cart and Cwidder (The Dalemark Quartet, #1)
by Diana Wynne Jones
Comfort reread. Why do I ship Kialan and Dagnar this time, lol.
I kept thinking about the way Moril is seen from the outside as sulky and teenagery in the 4th book. As usual, the way magic works is poetic and ineffable and not exactly spelled out even though Moril introspecting about it is a big part of the last half of the book. Moril seeing Hestefan and realizing that that's what he'll look like as an adult is a whole mood.