“Commoner Familiar” “Heimin no Tsukaima” (平民の使い魔)

Saito being sucked from Japan and into another world. When the summoning was comple he had a set of rune on the back of his hand. When he had to do battle with two-timing Guiche Valkyrie the rune glows and it let him use any weapon. He beats the Valkyrie and Guiche.