Sei P. Asagiri

A White Knight serving under the Valkyrie First-Response unit. Despite the White Knights' reputation, Sei is extremely kindhearted and truly believes in helping people. 
Although she isn't the sharpest tool in the shed, she can take care of herself and is one of the most kindhearted characters in the game. She's Stella's best friend and unofficial bodyguard.

Sei and Stella first met when Stella asked her father to take her to a "real kids park". The two formed a close bond and began to meet at the park regularly, until one day while they were there, a rogue White Knight took them hostage, on the run for undisclosed reasons. After being approached by the authorities, he began to gouge Stella's eye out and kicked Sei in the chest after she attempted to stop him, breaking several of her ribs and rupturing her organs, as well as knocking her out.

Afterward, Sei briefly regained consciousness to see the White Knight on the ground, not moving, whilst another had her slumped over his shoulder. He put his helmet on Stella's head and the two were quickly taken to the hospital. Sei was placed into emergency care due to the severity of her injuries and only woke up after Stella began punching her leg, telling her to do so. The two of them recovered eventually./