Sei-jun Ecstasy: XXX Shinai to Derarenai Heya de Mazoku o Buttaoshimasu

Story:

Ex, a failure of a hero whose holy light has yet to manifest, is ridiculed by his peers. But it turns out to have manifested in his dick! How is he supposed to defeat anything with that?! Even when his town is attacked, his crotch simply glows, and he's unable to do anything! While bearing the weight of these worries, a mysterious shrine appears before him...