The release date for volume 9 of Koisuru Boukun has not yet been announced. The previous volume, volume 8, was released on February 14, 2022. I do not have access to real-time information or future release dates, so I cannot provide an exact date for the release of volume 9.
To stay up-to-date on the latest information and release dates for Koisuru Boukun and other manga series, I recommend checking official sources such as the publisher's website, social media pages, or news outlets specializing in manga and anime.