New PvP Grounds Tome coming? Or some strange book boss?

[Yurai]

This picture was recently posted on the official FFXI Twitter:

FFXI_EN:
New enemies are awaiting for your challenge. http://t.co/xjGxNDQN #FFXI

At first I thought it looked like the players were attacking eachother, meaning some kind of PvP event. However it looks like the book is casting a spell, so this makes me think the black Grounds Tome is what they're fighting.

So is this just some new Voidwatch enemy, or some new system altogether involving black Grounds Tomes?