A rainbow kiss is a sexual act that involves the exchange of bodily fluids, specifically menstrual blood and semen, between two partners. It usually involves a person with a uterus and a person with a penis, though there are variations to it. The act involves simultaneous oral sex, like in the 69 position, while one partner is on their period. The goal is to climax together and kiss after mixing menstrual blood from one partner with the semen from the other partner in their mouths during the kiss. The combination of blood and semen is what creates a rainbow kiss. It is usually performed by consenting adults who share some sort of bodily fluids fetish. It is important to note that this act carries a risk of transmitting sexually transmitted infections (STIs) and should be done safely.