I had some thoughts about differences in time between the two worlds or whatever... Not completely sure, but it doesn't seem to matter anyway. It was just interesting how later in the game, an NPC in Motorville mentions that Oliver had been absent from school for a few days or so. But for the rest of the stuff...
1. How did Drippy hide a book in the fireplace when he was a doll? He's the lord high lord of fairies, one can assume if he has the power to telepathically communicate with other fairies in a different world, it wouldn't be a far stretch to get a book into a fireplace.
2. How did Oliver's mom know Drippy's accent and speech patterns when imitating him? Drippy was implied to be acquainted with Alicia. We can assume the reverse is true.
3. Drippy's explanation for why no one can see him/Esther/Swaine is because they're "from another world." So why can anyone in Ni no Kuniland see Oliver? He's from another world too. And then why could people see Drippy the doll then? It would also have been from another world. Alicia was from Ni no Kuni, but Oliver was born in Motorvile. Dual nationality?
4. During the time travel segment, chests that you opened in the future are already open in the past. Why? Plothole yes, but due to gameplay restrictions.
5. How is Shadar stealing the hearts of people in another world? Gateway?
And assuming your theory is correct, within his delusions caused by grief he manages to get over his dead mother after the Vileheart episode ... after which he continues to live in his dream world? People are thinking way too deep into this, going by Studio Ghibli's past record it's probably just your standard fairy tale.
If we were planning to discern the logic of a JRPG, we would be here for the rest of our lives.
No you wouldn't. All you would need to do is be able to acknowledge that the fictional story is what drives the game and details like who does Oliver's laundry or where he goes to school aren't relevant to the scope of the game.
Suspension of disbelief is a pretty important thing to learn with dealing with any kind of fiction.
This. People dont suspend disbelief anymore. Too lazy.