MIAA-384 Her sister became a stranded commuter due to the sudden downpour, and they stayed up all night together... Kirara Rin

I was considering marrying my girlfriend whom I live with. She has a younger sister named Rin... She is very affectionate and already calls me 'big brother,' chatting with me intimately. One rainy day, Rin came to our place soaked to the bone seeking refuge. ...A massive lightning strike caused a power outage, and when she clung to me, my rationality flew out the window, and we had raw sex right then... Despite feeling guilty, we kept satisfying each other in the bathroom, after meals, and all the way until morning...