To date, there are seventeen volumes in the True Tenchi Muyo! GXP series of light novels. Volume 16 was written by Masaki Kajishima, and has yet to be published outside of the main readership in Japan.
Seina is instructed in the basics of magic and learns that whether its plants or entire planets, their magically imbued significance limits access to them. Seina wants to visit one of these worlds, but that is complicated as most often only diplomats can be given permission from the powers that be.
According to Seina's mentor in this study, magic is not naturally occurring in the cosmos. Rather, it is one of the earliest manmade inventions from prehistoric times. As stated before, there are limits to how much magic can be used, much like in the piloting of Ryo-Ohki or another of Washu's creations.
Seina discovers that most of the cultures throughout the known universe that have access to magical abilities only do so because they lack the technological proficiency to duplicate similar results through more conventional science and engineering.
He is further warned against collecting magical components, as many of the plants under that category can behave like bioweapons. One could even venture that magic is used to terraform.
Seina is told that his recent sickness is common in children but not adults, and unlike Seina's long sickness, usually passes quickly. It happens when a child grows a magical organ that determines the child's magical capacity. Apparently Seina has grown a very large organ which suggests he will have significant magical ability.
The Renza gang are given a sham trial, despite Seto's best efforts to intervene. Washu sends Mimiko aboard the neutral planetary scale entertainment ship Racepshi. This helps them track down Kiriko, who is caught in the crossfire.
Mimiko and Kiriko meet up with Washu in the newly reworked Kamidake. Renza operatives express mixed feelings about Kiriko, leading into a back and forth of not only verbal taunts but holy weapon attacks. This quickly turns the situation on its head, and only by bringing out respective mech firepower does the argument finish decisively.