Crossover Trilogy (1 of 3) Siblings don't kiss

Part 1 of trilogy. A certain demon meets a girl like no other person he has met before. Curiosity makes him stay around this non-human woman that threatens to change his concepts of life, world and maybe love. They develop an unusual bond. There are notes at the end, some events are historically real. Sebastian is never mentioned by name, but we all know it's him. ;)