[Amaha Ririka's lesbian debut!] Ririka, an office lady constantly working overtime, is invited out drinking by her good friend and senior colleague, Yui, but misses the last train. Since Yui's house is nearby, she decides to stay the night. At first, the atmosphere is friendly, but as the night progresses, Yui can no longer contain her pent-up feelings and begins to seduce Ririka into lesbian love. Ririka is hesitant because she has a boyfriend, but Yui's sweet and gentle teasing gradually leads her to embrace the pleasures of lesbian love...