Summon Night Gran-These: Horobi no Tsurugi to Yakusoku no Kishi

One day, three children from a land known as Kusukusu summon two young heroes from faraway lands: Lost Ninebell, a skilled swordsman who has lost his memory; and Millet Tearbell, one of the Three Sages of Greybell, and the daughter of the high priest. Now bound by the summoning contract, these two must work together to help their benefactors and return home. (ebay)