First off, I'd like to thank 
Important Details.
As the release of the posting key will also allow those in possession to vote, the system for determining how much voting power is afforded to each member needs to be addressed:
Only vested members will be able to use the account's vote feature. Although any Niigata Steemian can post via this account, only members who have independently contributed Steem Power will be able to utilize this account's voting power. This should be done the same way as payouts are--in proportion to the user's vests. In other words, for now, the rule is, an investor in the account can vote once a day according to his or her vest proportion. If someone has invested 10% of the independently invested SP, then that user is allocated a 10% voting power upvote each day (or any amount of votes that equal 10% such as two 5% votes). This may need to be adjusted as the project grows, and also as we get a feel for the voting power of the account. We can discuss any changes that may need to be made in the SCN DISCORD CHAT.
Non-vesting members can still post via the account, up to two posts a day (the two-post limit also applies to all investors). Resteems of fellow Niigata Steemians' work can be unlimited, as long as double posting is not occurring. Before posting, always check that what you are about to post or resteem hasn't already been resteemed or posted by the account via another user. Non-vesting users will not receive a part of the weekly payout, but are free to use the account for exposure. If non-vesting users are found to be voting via the posting key (I really do not think this will be an issue) that user may lose access to the Steem City Niigata account.
Niigata users wishing to receive the posting key, invest, or who have other questions, please message me in the Steem City Niigata Discord Chat channel. I can give you all the details about how to go about doing these things there.
I think this project has tremendous potential for creating a powerful free market network of Niigata-based Steemit users.
For example, an English teacher could network with Japanese members in the area who wish to learn English, agreeing to transact in Steem via their personal accounts. The possibilities for growth by online and in "real life" are huge. This is not to mention the benefits of having the support of a group initiative here on Steemit.com as well.
That said, this is an ambitious endeavor and I need your input and feedback/criticism make it a success. With the blockchain as the common reference, I think we can make a fair, voluntary, and transparent system that to benefit everyone involved, and provide us with a nice little Niigata community and hub.