Ni no Kuni has horrendous ally AI.
Or to put it more succinctly, Ni no Kuni has horrendous AI for the systems it uses.
In Ni no Kuni, your characters tend to have relatively low Maximum MP totals compared to the cost of the abilities they use. When you’re directly controlling a character, this isn’t a problem – you make sure to use your abilities wisely and you run around and collect the MP restoration orbs when you have the opportunity.
However, when you’re not directly controlling a character & they’re under most AI modes, they use MP like crazy and don’t seem to get MP orbs unless they’re completely out of MP. It’s not unusual to have a character go from full MP to no MP in a single random battle.
There are ways around this. You can set everyone’s tactics to “Don’t Use Abilities” for regular battles, switch between characters and directly control the use of all abilities, and maybe switch to one of the ability-using tactics for boss fights. You could make sure that the characters you don’t plan to directly control only has monsters with cheap abilities so even if they use abilities like crazy at least they’re only losing 4MP per cast and not 25MP per cast. Or I guess you could try to stockpile large quantities of MP restoring items although this doesn’t seem too feasible as of yet.
Contrast this with your typical Tales RPG. Here, running out of MP is rarely an issue so it doesn’t matter that allies use abilities freely. Your allies go all out in each battle, letting the player focus on whoever they’re directly controlling confident that they’re receiving decent backup from the rest of their team.
The ally AI isn’t enough to ruin Ni no Kuni. It’s still a very enjoyable game with gorgeous visuals, fantastic music, a great sense of adventure, and fun writing. However, it also serves as a great example of how one relatively small design decision (low MP totals and only extreme MP use tactic options) can noticeably weaken a game.