Moto Saikyou Ansatsusha wa Inaka de Hissori Shinpu ni Naru: Dai Shusse shita Oshiego-tachi ni Shitawareru Ossan ga Anyaku suru Hanashi

Once feared as the kingdom’s legendary assassin, Zach “the Shadow” has abandoned his bloody past and now lives a quiet life as a priest of a rural church. There, he raises orphaned children and teaches them everything he knows: discipline, wisdom, and the combat skills to build a life outside the church walls.

When one of his beloved students—Emilia—returns with burdens she can’t conceal, Zach knows he can no longer hide and wait. Stealth and shadow are familiar aides as he begins a secret investigation into the troubles that haunt her. But while Father Zach may be content to fade back into the shadows, Emilia has other plans for the humble priest. She won’t stop until she drags him into the light—and reveals just how respected he should be!

(Source: J-Novel Club)