Pyre

Pretty straightforward in that you simply have to get a single character to level 5. By the end of my play through around 2-3 characters had reached level 5. If you’re struggling with this just play Rites using one particular character until you get him/her to level 5.

Alternatively, you can use Vocations to mentor a character to level them up faster, but I would recommend focusing on exhausting your private study (which grants attribute increases to your entire party) opportunities first before going down this route. This is to help you unlock Fear Not the Flame with Jodariel.