The Eminence in Shadow, Vol. 4 (manga) — Daisuke Aizawa

Cid is invited to Lindwurm, the Sacred Land, where a ritual known as the Goddess's Trial is held. Ancient warriors are summoned according to the strength of the challenger, providing an opportunity for honor and glory -- all the normie stuff Cid specifically wants to avoid! If his true strength is revealed, all his work to play the part of a nobody will be for naught...