In the moments that the Imperial soldier made for the desk, Kothar ran through his options to stop the soldier in his head. He could use his Spatial Portal to open a portal, but that would surely give away Kothar's identity to Docara. Next, he could use his Lightning Magic, but his more powerful spells took time to charge up, and there was no certainty that he could stop the soldier with a weaker spell.
Another option would be to lance the soldier clean through with his Plasma Blade, but that would leave distinctive scorch marks that would raise their own questions.
In the end, Kothar decided for none of these options, he hadn't practiced this before, but he was sure it would work, and besides, the Lightning Mana in the sword itself would do a significant amount of damage, additionally, there were Tribes people on the mission with them, and their weapons were similar enough to Kothar's that he could use it freely.