I NEED SEVERE HELP

What's the name of that manwa where that guy gets stuck outside in the rain and he like goes up to this tree or like rock for shelter and then gets turned into a girl and then ends up in a cave with one of his friends. Then his friends then his friend takes him back to like this cabin that they were supposed to be like at helping with his other friends.Okay, so like it's a full color and it's like basically they were on like a volunteer retreat and uh yeah, that's all I can remember.Okay, now, so this the book I'm talking about is like it's like really smutty and kind of juicy. And like one of the characters uh kind of okay, I don't know.Okay, still no. Okay, so basically when the guy is brought back to like the rest of the friends, one of his other friends kind of figures out that he's a girl because uh technically the guy was supposed to be helping them, but then he kept disappearing and another girl appeared and they and his best friend was saying that this girl was his sister or something. And then the guy, the other guy was like, that's not his sister and kind of blackmailed him and found out that the girl was just him and he was a girl. And so like he kind of like took him to like the bathroom and like you know, did the nasty or whatever.