The Light Clan (光の一族 Hikari no Ichizoku) is the clan where all Magical Girls were created. They are the mortal enemies of the Dark Clan.
The Light Clan and the Dark Clan had a war, fighting for centuries long. In the end, the Light Clan won the war and sealed away the Dark Clan's powers and luck. They cursed the Dark Clan with a 40,000 yen per month (around 370 USD) curse. According to Momo, the Light Clan had been hunting demons using a point-based system. Though this system still continues, most members are not as competative, thus not as hostile towards demons.
A City assigned to Sakura Chiyoda had served as a refuge for Dark Clan members wanting to lay low, before her disappearance 10 years ago. She would create deals for the demons to live normal lives under the radar within the area. Though a magical barrier is set up as protection from other Light Clan members until now, Momo Chiyoda has been shouldering the responsibility of protecting the City.
Magical Girls are the priests of the Light Clan whom helped the Light Clan win the war and seal away the Dark Clan. To become a Magical Girl, their physical body is entirely reformatted into an ether of magic. Due to this, Magical Girls must not deplete their mana, or else the bonds holding their body together will disappear and they shall dematerialize. When dematerializing, they do not die, however their soul will remain as scattered particles in the air unable to obtain a physical body.
Each Magical Girl possesses a core which serves as a base for their mana. In case they have lost their physical body, with enought power, this core may take some magical form so they may live on in some way. Furthermore, their Magical Girl form comes with its own Light Clan name, costume, weapon and special move, it improves their overall performance and abilities. Besides that, each have their own navigator to assist with their duties as well.
Additional abilities not exclusive to the Light Clan include activating magic circles (symbols that can be hung on doors to form barriers), and creating physical vessels and familars. These can be performed by anyone within the Light or Dark Clan with the proper use of mana.