Five major empires coexist on the continent of Istuka. The bloodlines of the nobles and rulers here generally contain a special power called spiritual power. No one knows where this power comes from. It gives birth to a type of special ability user called a spirit slayer. For many years, the five empires have been at war. However, due to bloodline constraints, the main force of each country is still the ordinary regular army. Against this background, the Central Empire in the middle of the continent launched the Crystal Sky Project in order to create a large number of Soul Slayer troops with the power of bloodline. However, many years of research almost ended in failure until the only successful experimental subject, Seri, appeared...
