In tower is a boss, after beating the maid and level up several times you can trey to beat her mistress, she wont atack on her full power but you need some power to beat her, after that she will give you a blessing or item and some of them increase spirit, but yes 26 is pretty big there, sorry for bad english and her blessings and item usually have some debaffs like increased sensivity and else
Thanks, actually i think that there like 5 places where you can raise your spirit, but i not sure, blue room at temple, maybe vivian, boss in tower, maybe church, aaaand, oh! Items, some items from shop actually raise up your spirit, pretty ironical how i said it, but yes, i think that it is all of them, if we wont count just level ups
So, notably this isn't possible on hard mode (you can't go over 3 starting spirit) and can only be taken once from Sophia. There's also the runes, as you mentioned, Vili's Wisdom perk, the teachers pet perk, three levels of "spiritual reserves" perk from levelup, and the nymph's blessing. Most of these (Vili, Sophia, and Teachers Pet) all have negatives, but are fairly easy to mitigate.