According to Osho, no form of sex is entirely free of violence; conception and even the very urge to be born carry inherent violence. Life itself—eating, breathing, moving—inevitably harms other life. The only possibility is to minimize it: lessen craving, act with awareness and responsibility, and, ultimately, dissolve the desire that perpetuates birth; when all desire ends, rebirth ceases.
There’s no 100% harmless sex because living always hurts something a little, so be gentle, want less, and over time let the wanting fade.