My serious sister, who has nothing to do with eroticism, discovered my masturbator! She kept asking me how to use it, so I demanded that she demonstrate it to me and use it as a wank! Then my sister showed me her panties and breasts! I got carried away and ejaculated on her, and she secretly got horny... Furthermore, when my sister found out that using the masturbator too much can cause ejaculation disorder, she forced me to train her to ejaculate inside her vagina, claiming that it was for her brother's sake, to relieve her frustration. She felt so good that she no longer needed the masturbator...