Eien no Aseria - Spirit of Eternity Sword - S01

Yuto Takamine and his younger sister-in-law Kaori were visiting their parents' grave when they were abruptly pulled into another world called Phantasmagoria. There, the King and a woman named Restina seized Kaori as leverage, forcing Yuto to fight their enemies. The King handed him a sword named Motomeh and tasked him with defending the kingdom from hostile spirits, promising Kaori's freedom only if he complied. With no other choice, Yuto set out on his perilous journey.