When they were in middle school, Souta, who was a dear friend of Riku's, pulled a prank on him by planting a kiss on his lips. This act made Riku develop romantic sentiments towards Souta, but he decided to keep them hidden and continue their friendship. However, after consuming alcohol, Souta's demeanor towards Riku altered, causing him to question if they engaged in anything inappropriate because his memory of that night was hazy.