Byston Well Monogatari: Garzey no Tsubasa

Tales of Byston Well: Garzey's Wing

Christopher "Chris" Chiaki is an easygoing guy who keeps failing his college entrance exams well into his mid-twenties. His days are occupied with Kendo practice, visits to his family's shrine, and dreaming of his high school reunion. When his spirit is suddenly transported to the world of Byston Well, Chris becomes Garzey's Wing, a legendary holy warrior. The Metomeus tribe summoned him to help liberate them from slavery, but unfortunately, Chris has no knowledge on how to be a holy warrior, and moreover, only has an incredibly dull sword which he salvaged from a corpse.

To make matters more complicated, there is another Chris who is still in the normal world! He cannot control the events in Byston Well, but is tied to the fate of the other Chris. The young man must struggle and adventure in a world of magical creatures and mysterious foreigners.

(Source: MAL Rewrite)