Going by the maximum amount stated above, the buyback would set them back by about 1.22 billion $, which probably constitutes something like 8-12 % of their total cash reserves.
Correct, it's just shy of 8% of their total assets, or a reduction of about 10% of their net assets (most of which are short-term investments and cash). And the poster above is also correct that they are kept and marked as treasury not cancelled - adding to an existing 13.8 million shares in treasury (or about 10% of the company).
Assuming Nintendo buys another 8% of the company later this year as the shares tank owing to non-recovery of the Wii U - 26% of the company could be sitting in treasury shares - perhaps more if Iwata keeps buying up more and more of the company. At a certain point the company could become much more viable for a management buyout.
We also don't know the exact power of treasury shares in NCL and whether management can exercise them at all - but what we know is that if infact someone attempts a hostile takeover, NCL could use the treasury shares to prevent that from happening by (one example) trying to find a party to acquire those shares with a mutual shareholding/buyback agreement.
Also, the existing parties in Japan that own Nintendo stock may also have certain restrictions on their ability to vote or have effectively assigned existing management the right to vote on their behalf. These kinds of shareholding agreements are relatively common in Japan.
Anyways IMHO if someone were infact stupid enough to attempt a hostile take over of NCL, they would be digging their own graves since talent attrition would end up killing the company - the IPs aren't as valuable as everyone thinks - Mario is relevant because of the talent behind it that has kept producing great games.