I saw both in a run and in a guide here that after Medusa fight Yuri's equipping 'Magic' skill, along with 'Combination'. While I get the latter, does 'Magic' actually affect characters who don't use spells?

Artes other than spells can use the matk stat https://aselia.fandom.com/wiki/ToV_-_Yuri_Lowell:_Artes