Shakugan no Shana (2005)

Murdered by a demonic being, 15-year-old Yuji Sakai has his life force replaced by a flame that dims with each day. When the flame dies, no one will remember he was ever alive. This is how he meets Shana: a warrior with a burning sword, and the will of a god as her guide. The two form a bond as Yuji becomes Shana’s accomplice in her battles to keep the balance between the ordinary world and hers.