Nanatsu no Taizai: Seven Days

Set in the land north of Britannia, there is a certain forest where humans are prohibited - the Fairy King's Forest. Harlequin, the Fairy King, has not been seen by anybody for the last 700 years. His younger sister Elaine guards the Fountain of Youth from human greed. After several separations and 700 years of isolation, her tears are about to dry up anytime. All of a sudden, a young man named Ban appears, looking for the Fountain of Youth.