I find it humorous that he's upset with Reito on his demotion & pay cut when he himself is the reason why he's in this predicament.
characters like him aren't exactly known for their introspection or self-awareness.
The Numbers in your bank arent real though. Its just 0's and 1's.
I'd highly doubt that somebody could even attempt to draw 10 Mil without waiting for weeks.
You might not be able to pull the amount physically from your account in the form of bills and coins, but that money is
definitely real in the sense that the banking system treats it as real, and uses it constantly in their own forms of lending/borrowing and allowing it to accumulate its own interest within your accounts.
Money, even digitally-represented, is never stagnant within an economic system. Arguably the only way money is
never being constantly used is when you have literal bills & coins stuffed in a sock in your mattress.
And someone has to be able to pay him those billions monthly, and
that has to come from somewhere else, without crashing the entire system through either sucking up all of the financial ability of the country of Japan, or through hyper-inflation and the depreciation of their currency due to over-production to meet the sheer quantity.
But I think the real problem is there's no stated context for how the current global economy works. We know that mana stones are essentially the new power source of the world, and adventurers are relied upon to provide them, and they're distributed to countries according to the amount brought into the "central pot" by each county's adventurers.
So Reito is effectively providing half of Japan's total energy supply, in that sense. That
would justify the amount of money he's bringing in, if you think about how much electricity/energy modern-day Japan consumes, and how much money is spent to provide that amount to the total populace.
All of that going to one individual, puts this into more easily-understandable context, I think.
But also, that means that him "retiring" is halving Japan's total energy production, so I think the country would be fucked in an entirely different way, at that point.
Which is why the system of relying on individuals like this to power society is a bad idea, when one dude quitting would cause such massive systemic issues.