Shindou Setsuna

She and her sister were unexpected births in the demonic cult which had abducted their mother for use as a breeding vessel. The church managed to smuggle them out and train them as exorcists, so the cult and their leader opted to bide their time until the girls were ready to resume the role their mother had originally assumed.

Because of the way the "vessels" are impregnated, it is very possible Setsuna and Yuuka are half-sisters. They do not look alike and have very different physical attributes.

If Setsuna loses hope after the school gang bang scene, she is taken back to the demon cult and eventually gives birth to the next generation of breeding vessles. If she vows to keep going, Touma eventually succeeds in rescuing them with help from the Church. Despite everything she and her sister went through, they vow to continue their work as exorcists.