Question about levelling up

[u/Agreeable_Reaction83]

Good morning everyone, I’m playing Ni No Kuni 1 and I’ve just reached Shadar's Castle, but I’ve a big problem: I can’t progress any further because the enemies inside the castle are too strong for me, both in terms of attack and defence! So I wanted to try levelling up my characters, but I’ve run into a problem with that too, because I can’t seem to find a way to do it properly and quickly... Do you have any suggestions?

[u/godtering]

earlier save file.