My serious sister, who knows nothing about sex, finds my fleshlight! She keeps asking how to use it, so I demand a demonstration to get her aroused. She shows me her panties and tits! Then, I cum on her and realize she was secretly aroused. She learns that overusing a fleshlight can cause internal ejaculation issues, so she trains me to ejaculate inside her to relieve her sexual frustration. Now, I don't need a fleshlight anymore.