Maybe the friend has a scientific experiment gone wrong. They were working on some kind of gender - changing device or formula. And instead of testing it on a proper subject, they accidentally use it on their friend. As a result, the friend who was a boy is now a girl. This would cause a huge upheaval in the person's life, from relationships with family and other friends to self - identity issues.
In a more supernatural or fairy - tale - like story, a friend might be a fairy or a wizard in disguise. The friend might have made a deal with some other magical being that requires turning someone into a girl as part of the bargain. So, the unlucky (or lucky depending on how you look at it) friend is turned into a girl. At first, the character might be shocked and dismayed, but as time goes on, they might discover new aspects of themselves and even enjoy this new form in some ways.
Chapter 139, "Resource Gap, Changes in the Camp [Three-in-One]", is the clearest early answer because it turns Xu Ning's situation into a concrete plot event. The setup is The ones breaking through now are the second batch, mostly aged..., but the pressure keeps building through This batch is just beginning, and I estimate that within a month,.... Once the chapter lands on I've looked at these people;
Chapter 144, "Self-serving at the Expense of Others, He Meng's Furious Rage [Sorry for Being Late]", is the clearest early answer because it turns Teng Jiao's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Don't touch that Teng Jiao, it's poisonous!" "The Hunting Team's... and follows through with Everyone goes to the south to find, find Great Xia's camp, we must....
Chapter 505, "Another Intelligent One", is the clearest early answer because it turns Damien's situation into a concrete plot event. The setup is The forest had gone quiet again but it was not in any way peaceful., but the pressure keeps building through This was the silence that came after prolonged slaughter, when even....
Chapter 114, "New House, New Rules, New Starting Point [Four-in-One Mega Chapter]", is the clearest early answer because it turns Cold Beasts's situation into a concrete plot event. A useful checkpoint is the way the scene starts with In fact, the moment the rodent swarm appeared on the north slope of... and follows through with Thinking too far ahead!" Xia Hong chuckled softly, shook his head,....
Chapter 141, "Intermediate Thunder Kui, Second Reshaping Skin [Three in One]", is the clearest early answer because it turns Giant Axe's situation into a concrete plot event. The chapter gives readers a real answer by opening on It's a pity that Xia Hong and the fourteen members of the Hunting... and ending on Based on the speed and power of the Snow Mane's spikes and the....
Chapter 68, "Coal and Iron Mines", is the clearest early answer because it turns Yue Feng's situation into a concrete plot event. It opens with Over two hundred people began working together, and the once ravaged... and closes on In the makeshift wooden house, without any proper arrangement,....
Chapter 521, "Storming The First Base II", is the clearest early answer because it turns Damien's situation into a concrete plot event. Early on, He had walked less than a kilometer from the abandoned stronghold.... By the end, The creature roared and released a shockwave of dark essence outward..
Chapter 146, "Rage, Murder, Ferocity", is the clearest early answer because it pushes Cold Resistance Level into a new phase or setting. Early on, First Year of the Great Xia, February 25th On the third floor of the.... By the end, Though the wood was fine, seeing the population short by eight made....
Chapter 11, "Powerful and Cunning", is the clearest early answer because it turns Rogel Camp's situation into a concrete plot event. Early on, It's certainly not true to say one isn't envious of this Snow Mane.. By the end, This terrifying scene sent a chill through everyone's hearts..
Chapter 46, "After modification: Chapter 46 Wrong, there's an issue [Please follow!]", is the clearest early answer because it turns Xu Ning's situation into a concrete plot event. Early on, Hearing Shi Qing's polite request to leave.. By the end, After the alarming incident of the deceitful monster attacking Xia....