The Boy with the Cursed Boar's Head

Setsuna is a quiet girl living with Grandma whereas her parents were drowned in a tsunami when she was an infant. When she finds Grandma devoured by a demon, Setsuna finds a mysterious hole inside a bush in the middle of the forest, and once entering it, she discovers that she went into Eden - a magical land where anything is possible beyond wonders. As she takes a look around, she is caught in a war between the Edens and the Demons, an evil and immortal race led by Muzan Kibutsuji, a 10,000-year-old demon who wants to rule Eden Castle. Hired and trained to become a Demon Slayer of Eden Castle by Queen Kotoha Hashibira, Setsuna is instructed to destroy Muzan and his army. She comes across Inosuke, a 15-year-old teenaged boy whose head's been swapped for a boar's by Muzan since he was raised by boars. Despite him being short-tempered, Setsuna reluctantly teams up with Inosuke to defeat Muzan, however, little do they know a romance blooms.