I assume re: the belt that Chimera, like most other phantoms, is within him now; the belt is how he feeds the Phantom within his body.

Though I wonder how long it'll be before they realize that Haruto could just give him mana, and problem solved!

Not necessarily. There's three problems with that.
The first is that we don't know how much mana a common Phantom contains. We can't just assume the mana Haruto has to spare will be enough to feed Chimera.
The second is that, by constantly leeching off Haruto, Wizard will be much weaker. You have to remember that he has to commonly replenish Koyumi as well.
The third is that I don't think Nitou would want another man's hand so close to his crotch on a daily basis :p

Regarding if Haruto can give Nitou the mana he needs to sustain Chimera, I like to think Phantom mana is special.

I think Chimera might have something ageist phantoms, because he was partnered up with an other wizard from ancient times or something

No. Why you ask? Because reasons!

My theory is that Chimera is just super picky about what he eats and he'd rather eat something with a little more substance i.e. a whole Phantom. :lol

The correct answer is he doesn't want to put his hand on Haruto's crotch.

So I watched this episode on Tuesday. I'm only chiming in so late because 1) I had a hell of a week and 2) I was kind of bored. After the excellent Medusa arc we just had it just felt kind of flat this week.

If they'd foreshadowed this guy finding the ring and magnum maybe over the course of a few episodes, seeing a shot of him at the end of each week on his way back to Japan then maybe I would have liked it more. I just felt there wasn't enough build up for this. And it was obvious he was going to steal the belt, I guess Nitou is just kind of dense.

... That moment when you realize that Kamen Rider Beast is secretly the plot of Ryuki.