Katainaka no Ossan, Kensei ni Naru Gaiden – Ryuu Soken no KisekiKatainaka no Ossan, Kensei ni Naru Gaiden - Ryuu Souken no Kiseki; 片田舎のおっさん、剣聖になる外伝　竜双剣の軌跡; From Old Country Bumpkin to Master Swordsman: The Twin Dragonblade's Journey to the Top; From Old Country Bumpkin to Master Swordsman Side Story: The Legend of the Twin Dragon Swords

Serena, a Platinum-ranked adventurer, once trained under the legendary Beryl. One day, she takes on a routine goblin extermination request in a remote village. However, the request comes with an unusual conditionshe must train a young girl, Nell, to become a proper adventurer. Nell, inexperienced and unable to defeat even a single goblin, dreams of becoming an adventurer for a reason she refuses to share. Though initially hesitant, Serena sees a spark in the young girl and takes her under her wing. As Nell struggles to grow stronger, Serena herself continues her journey, overcoming countless battles and challenges. This is the story of Serenas rise to the peak of the adventurer ranksBlack Rank, and the bonds she forms along the way.