Synopsis: Issho ni Ken no Shugyou o Shita Osananajimi ga Dorei ni Natteita no de, S-Rank Boukensha no Boku wa Kanojo o Katte Mamoru Koto ni Shita

一緒に剣の修行をした幼馴染が奴隷になっていたので、Sランク冒険者の僕は彼女を買って守ることにした / My Childhood Friend Who I Used to Train Swordsmanship With Became a Slave, so I, as an S-Rank Adventurer, Decided to Buy and Protect Her / Issho ni Ken no Shugyou o Shita Osananajimi ga Dorei ni Natteita no de S-Rank adventurer and second-generation sword saint, Ryunoa Styler, is reunited with his childhood friend, Aine, who has been reduced to slavery. Ryunoa purchases Aine in order to save her, however, she's been given a cursed collar that causes the wearer to go into 'heat' once a day...