Background
An aide to the Pantoran senator Riyo Chuchi, Sei is deeply committed to supporting independance and to the rebellion. She did not come from a terribly priviledged background, she ended up as the senator's aide via a mostly-faked application to their diplomatic corp, citing an entirely fabricated glowing educational resume. Most of her education was from sneaking into libraries at night and streetsmarts.
Once in the diplomatic training programme, however, she excelled. So much so in fact that there were grumblings from the other recruits. An investigation showed no cheating on her part, but it did reveal her deceit getting in.
Rather than being outraged Riyo was delighted and hired her as her aide, knowing she could rely on Sei for the more...pointed end of diplomacy.
Motivation