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

Story:

Ryunoa Styler, an S-Rank adventurer and second-generation sword saint, meets up with his childhood friend Aine after learning that she has been sold into slavery. Ryunoa buys Aine in an effort to save her, but she has a cursed collar on that sends the user into a "heat" once per day. The struggle for Ryunoa to find a means of removing the collar has begun!