Kirawaremono no Tenisha wa, Demodotta Isekai de Dekiaisareru

Thirteen-year-old Towa, suffering from a severe case of "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 otherworlders. To hide his lack of powers, he puts on an arrogant front, which ended up pushing away even the person he secretly admired, his own guard knight, Griz. One day, he was attacked from behind. "I've been killed!" he thought—only to wake up back in his original world. Fifteen years passed, and he lived a mundane life as an ordinary office worker, haunted by memories of Griz. Then, he suddenly found himself lost in that other world once again! Determined to live a quiet life this time, but for some reason, Griz, whom he's reunited with, keeps closing the distance between them...? Source: MU