Source: sanspo.com article, dated March 1, 2006
Basically, this is all about how when KAT-TUN's original tour dates were announced, the 433,000 total available seats were snapped up in *one hour*. So they have now decided to add 200,000 more tickets in the form of additional shows.
There's a table accompanying the article. My guess is that most of the additional shows are afternoon ones at the venues on days where previously there was only a single evening show.
What made me totally take notice was the last two dates of the table:May 13-14, 2006 @ Tokyo Dome
Yes, they are returning to the Dome a full week after they finish Yokohama. I've no idea at this point how many concerts they'll perform at the Dome over the two days, but this looks pretty impressive that they are finishing at the same huge venue that they're starting at.
And the last paragraph says KAT-TUN will be performing "Real Face" on Music Station on March 10