Four adult college coworkers are hopelessly in love with 36-year-old part-time worker Ayumi. Seeing her bare G-cup breasts in the mixed bath leaves them painfully hard, and her gentle willingness to pamper them only makes their desires escalate. The trip moves from a group encounter in the hot spring to outdoor sex after one man confesses his love, helping a virgin through his first penetration, and finally a drunken five-person orgy with all four admirers.