Methone and Ymir were tertiary class pallasites. They are not a human. As a pallasite, their time control and another powers, depends of their weapon (sickle) and with out it, the distortions made by their disappears.
They are twin male brothers. Cyllene has a brown hair, and Graip has a black hair.
Titan and Aegaeon send the two brothers to kill the bronze saints before they arrive in Pallas Belda. Theyattack Subaru and he falls in a abysmal. Haruto goes save him (he fell in a forest) and Greip with Cyllene go kill the two bronze saints (the two parasites compete to see who kills first Subaru), and Haruto gets away, and after, Subaru (injured) gets away too. Clean and Greip find Subaru and mocks him because Haruto left him alone; but, Haruto appears and defeats Greip, and Subaru defeats Cyllene. They get away.
After, in Pallas Belda, after Celeris death, the two attacks the bronze saints in the sewer, and Subaru arrives with the Equuleus Cloth (wore for the first time by Subaru), kills the pair of pallasites.