Flag of Regalia: Seitenkenrei no Hime to Gin Kaminari no Kishi

is a Japanese light novel series written by Hoshisan Hana Moyu, with illustrations by kylin. The series began publication on June 9, 2017 by ASCII Media Works under their Dengeki Bunko publishing imprint.

Synopsis
The ancient city of Kushur Lind, where fierce battles with neighboring countries continue. Soldiers gathered from all over the world and the ancient humanoid weapon "Anti-Dragon Single Horse" are crowded together. Senki Artone, who went to this place for encouragement, met a boy who lost one arm in the battle. His name is Inazuchi, and he regrets that he wanted to fight with the princess.

A feast is held for the princess that night, but in the midst of the bustle, there is also a female clan named Shinmild. Their purpose is to seize the "Anti-Dragon Single Horse" excavated in the ancient city and take the life of the princess.

As the princess approaches the sword, a single dragon that shoots silver thunder suddenly appears and saves the predicament. What emerged from the giant was a silver-haired girl who had the image of a boy she had seen before.

The encounter between the two may have been a blue sky. But it was a fateful encounter.