[Drops!] I'm being taken by my girlfriend's sister. Motion animation

Overview： His girlfriend,who he lives with,is a selfish and self-centered woman. She doesn't seem to like sex,so he's still a virgin until now... On top of that,she exploits him like an ATM and even threatens him,so he even thinks about breaking up with her every day. He's on the verge of exploding with the stress building up and his sexual desire that he has nowhere to vent,but the only thing that he finds comfort in is the presence of her younger sister,who lives with him because their school is nearby. One day,by chance,he ends up in a sexual relationship with her kind younger sister!? "What do you think,big brother? Which feels better,your older sister or me?" Contrary to her usual innocent behavior,she approaches him in a devilish manner in this reverse NTR motion animation!!