Senketsu no Elf  

Elvenblood, 鮮血のエルフ

In essence, what was left for the boy was only the girl, and vice versa. These were human siblings living in a remote village and elven siblings residing deep in the forest. Despite not being friends initially, their peaceful coexistence continued until the sudden invasion of elves on the human world disrupted their bond, causing them to diverge. Eventually, Imina, a human boy, and Ellis, an elf girl, found themselves facing each other on the battlefield, with Imina wielding a crimson sword that would continue to flow with blood-colored energy. Thus, the dark fantasy tale begins here.