Issho ni Ken no Shugyou o Shita Osananajimi ga Dorei ni Natteita no de

Lunois Styler, an S-rank adventurer known as the "second sword saint," reunites with his childhood friend, Aine, who has fallen into slavery. Lunois buys Aine to save her, but she is fitted with a cursed collar that causes the wearer to "go into heat" once a day? Lunois' fight to find a way to remove the collar begins now!

(Source: Micro Magazine-sha, translated)