Kirawaremono no Ten'isha wa, Demodotta Isekai de Dekiai Sareru

Thirteen-year-old Towa, suffering from a persistent "Chuunibyou" syndrome, is suddenly transported to another world. Although he is a rare foreigner in the new land, he has yet to manifest his "gift"—a unique ability granted only to outsiders. To hide the fact that he lacks this power, Towa puts on an arrogant front, earning the dislike of those around him, including Griz, his own guard knight. Depressed and disheartened, believing that even Griz, whom he considered his only ally, despises him, Towa is attacked from behind. When he wakes up, he finds himself back in his original world, but fifteen years have passed. Haunted by memories of Griz, he now lives as a simple businessman. Yet, for reasons unknown, Towa finds himself drawn back into the parallel world once again...

(Source: Kadokawa, translated)

Note: Includes two extra chapters.