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

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...