The transformation might occur due to a curse or a special power that the boy acquires. It could also be a result of a wish that backfires in an unexpected way.
Perhaps the manga boy undergoes a psychological or emotional change that leads to him presenting as a rauchy girl. Maybe he's trying to escape a difficult situation or find a new identity.
Chapter 399, "Wait Until I Am Rich", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event. The setup is Seeing Jiang Zhao Yuan's astonished expression, Jiang Li smiled and..., but the pressure keeps building through I'm not plotting against the company..
Chapter 615, "River·Doraemon·Li", is the clearest early answer because it turns Doraemon's situation into a concrete plot event. The setup is Everyone huddled close with their bowls in hand., but the pressure keeps building through Outside, the storm was rampant;
Chapter 684, "It doesn't matter if it gets broken, I have the money to fix it.", is the clearest early answer because it turns Luo Xingmu's situation into a concrete plot event. It opens with But Jiang Li had already evolved; she was now a film producer who...
Chapter 460, "Saving People", is the clearest early answer because it turns Hua University's situation into a concrete plot event. It opens with [HAHAHAHAHAHAHA, Jiang Yan is impersonating me.] [At this moment, I... and closes on Dare to attack me in hiding?!.
Chapter 335, "You would be incredibly fortunate if you could get connected with the merchant family!", is the clearest early answer because it turns Lin Manru's situation into a concrete plot event.
Chapter 515, "You actually kidnapped a man?!", is the clearest early answer because it turns Su Yinwan's situation into a concrete plot event. The chapter gives readers a real answer by opening on After Miss Su Yinwan left in a huff, Shang Shuyue's mood greatly...
Chapter 615, "River·Doraemon·Li", is the clearest early answer because it turns Shang Shaojing's situation into a concrete plot event. The chapter turns that into something concrete by moving from Everyone huddled close with their bowls in hand.
Chapter 648, "Even Wild Boars Make Way!", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. It opens with Jiang Li also casually picked up a tree branch and then directly... and closes on This is just a program performance!] Jiang Li and Brother Pei....
Chapter 316, "Zhao Lang Gets Jealous", is the clearest early answer because it turns Zhao Lang's situation into a concrete plot event.
Chapter 854, "These Brothers Are Quite Lacking in Love", is the clearest early answer because it turns Ji Yanbai's situation into a concrete plot event.