Seiran Shi started as a low-ranking army officer and the sole remaining retainer in the Kō household. Seiran was taken in thirteen years ago by Shōka Kō, and he has made a vow to spend his life repaying that kindness.
He helps the Kō family by protecting them at their home, performing repairs on the family estate, and taking small guard jobs to earn money. He is a very skilled fighter and swordsman and is usually found following Shūrei to guard her, even when she doesn't know it.
Seiran is later revealed to be the previously exiled second elder brother of Ryūki, Seien. He then discreetly protects the emperor by guarding him and giving him hints on decisions to be made, as Seien was often referred to as the son with the greatest potential to become a good emperor in his childhood.
Seiran is very secretive and keeps to himself most of the time. This makes Shūrei worry about him because he doesn't talk about himself much, while she talks to him about everything. He conforms to the idealism of "the end justifies the means".