Tosca is an old friend of Yuuto Kiba and another survivor of the Churches Holy Sword Project.
Tosca is a young woman who is the around the same age as Yuuto, but has the body appearance of a teen due to being trapped in a barrier that halted her ageing. She's also described as to having white hair tied into twin tails.
Tosca seems to be a normal girl but is new to her surroundings and so feels taken aback, although she is taking in things at a small pace, learning Japanese and going to school.
Tosca was an orphan taken in by the Church and one of the few children chosen to take part in the "Holy Sword Project" supervised by Valper Galilei where he performed human experiments on them. However, Valper later disposed of the children who took part in the project with the exception of Yuuto Kiba who escaped, and Tosca, who had survived due to being protected by her Sacred Gear which she had awakened at the time, sealing her in a barrier that halted her ageing. Researchers then had no choice but to place Tosca into a deep hidden chamber within the facility.
She first appeared at the end of Volume 19, as one of the of the followers of the Church rebellion where Vasco reunited Tosca with her old friend Yuuto Kiba, where the two then shared a heartfelt hug after being apart for so long.
Tosca was mentioned in Volume 20, that she occasionally visits the Hyoudou household being taken care of by the girls as well as learning about Japan from Rias, Asia and Koneko. She was also introduced to Kiryuu by Kiba and Asia, who she also became friends with and taught her a lot of things, although Issei is worried that she might turn her into a perverted girl. Tosca is also noted to have gotten along well with Valerie.
Barrier-Type Sacred Gear: A Sacred Gear with the ability to create shields and barriers that could last for years. Those within the barrier are left in a suspended animation, preventing them from ageing and don't require food or drink as sustenance to live. However, Tosca currently doesn't have full control her Sacred Gear as she had trapped herself in a barrier for years, leaving her un-aged since then.
- Tosca is most likely Italian as her name is Italian.
- The place where she was born is most likely Tuscia, Italy, as revealed in the meaning of her name which is said to be derived from the Late Roman by-name Tusca, the feminine form of Tuscus, meaning "from Tuscia" or "Etruscan".
- Her exact birth place being the only village in Tuscia which is the village Castel Cellesi.