GVH-685 Sister and Her Friend Watch Brother Masturbate, Then Swallow His Cum

Nanao, an office worker, is caught masturbating by his sister Rina, who asks to see his penis. When he ejaculates, she reflexively takes it in her mouth and swallows. Later, Rina's friend Konatsu does the same. The two girls then treat Nanao as a toy for their own curiosity, forcing him to participate in their 'studies'.