L.D. 250 is a woman in her early twenties, with long hair tied back and wearing a cheap track suit. She wears no real makeup. Just like a shut-in who had forgotten how to interact with other human beings, she has lost any distinction between at-home clothes and outside clothes and she essentially wears pajamas year-round. Although it's impressive in a way that she can still attract others despite completely losing the ability to focus on herself as an individual. 
L.D. 250 is someone who's only focused in moving forward, never thinking about the past. She has also lost the ability to focuse on herself as an individual. Presumably she's as devoted towards the White Queen as the other members of Guard of Honor are.
Light Novel Volume 01Edit
L.D. 250 was one of the summoners standing guard in Toy Dream 35's tunnels as they completed their project. As she talked to another Uniquely Selfless about the upcoming conflict with the major summoner factions, all lights on the area went out at once. L.D. 250 heard somone breathing nearby, so she reached for an Incense Grenade before realizing it wouldn't have any effect if she couldn't see the enemy with the naked eye. She was then knocked out by Kyousuke Shiroyama's Blood-Sign.
L.D. 250 is a veteran summoner. She was previously a Freedom ace summoner with 954 Awards, and was also part of Government and Illegal in the past. She is one of Guard of Honor's three 900+ instructors, together with Azalea Magentarain and an unnamed summoner, which trained the organization's new summoners, managing to raise at least 70 of them to the higher 800s.