Goblin Slayer Side Story: Year One, Vol. 1 (manga)

Three days after his sister’s death, he finally regained the will to move. In the aftermath of a goblin raid, a lone boy mourns the loss of his village, his family…
Five years later, that same boy visits a city on the frontier and becomes an adventurer.
Despite being the lowest rank and wholly inexperienced, the young adventurer immediately accepts a quest and sets out alone to raid a goblin lair. His mind already burning with a clear vision of his calling, the legend of Goblin Slayer begins!