Kakusansei Million Arthur: Gunjou no Sorcery Road (Manga)

is a Japanese manga series written and illustrated by Fuugetsu Makoto. The manga was serialized in the Dengeki Daioh magazine and published in Japan by ASCII Media Works under the Dengeki Comics NEXT imprint from January 2014.

Synopsis
In a strange twist on Arthurian legend, young Art pulls the magical sword Excalibur out of a stone--only to find himself as one of a million Arthurs, fighting to defend the island of Britain from enemies and to earn the rank of the true king. Art is pretty puny, but his childhood friend Ligu (who was also chosen by an Excalibur) tries to keep him from being immediately killed.

Soon Art lives in a castle with knights, which are created beings who serve the kings. From the respect with which he treats the knights, he inspires some to hope he becomes the true king. But is that really achievable by a scrawny crybaby like him?

(Source: MangaHelpers)