To date, there are seventeen volumes in the True Tenchi Muyo! GXP series of light novels. Volume six was written by Masaki Kajishima and is not available in Western markets.
Something distracts Ryoko Balta from her boredom. Her ship is in the middle of routine maintenance at a space dock within towing range of the academy proper. One of her crew members has met with her to discuss research on the Kamidake ship series that was leaked.
Balta devises a plan, and uses her Erma disguise to lure Seina and the Kamidake into space.
And in so doing, her ship must dock again for repairs. At this point, Balta feels defeated.
Later, after browsing a lingerie store with Amane, Seina makes good on a date with Erma. When they meet up, one thing leads to another, and Ryoko Balta reveals herself before him.
Airi later explains to Seina and his friends that she has known of Erma's secret identity for some time, and that she was used to purposefully lure pirate activity into GP patrols. Seina takes the Kamidake on another test run, in which he intercepts a GP operative trying to deliver something of critical value to Lady Seto.