The Prince of Tennis: Golden Glitter

Nan Ji, a seemingly ordinary sixth-grader, was an avid Fate/Grand Order player in his original world. He was obsessed with the game's Heroic Summoning and historical adventures, and particularly with the mythical hero Gilgamesh, for whom he held a near-worshipful devotion. However, by chance, while summoning another Heroic Summoning late at night, a dazzling light enveloped him...