My childhood friend who I used to train swordsmanship with became a slave, so I, as an S-Rank adventurer decided to buy her and protect her.

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)