Simon & Schuster senior editor Christian Trimmer remembers the first time he read about transgender teenage couple Katie Rain Hill and Arin Andrews. He was touched they had found each other. “There was something so beautiful about the universe being on the side of these kids,” he recalls. “When so much of your life is changing, and you’re forming your sense of self, it’s always helpful to have someone who gets you, and with Katie and Arin that was absolutely the case. They understood each other from that first meeting.”

Trimmer initially approached the Oklahoma couple about co-writing one book, but ultimately they collectively decided it was best for each of them to tell their own stories. In September, Simon & Schuster will release Katie’s memoir, Rethinking Normal, along with Arin’s, Some Assembly Required. Both books document their painful experiences growing up in the wrong bodies and their transitions (20-year-old Katie was born male, and is now female; Arin, now 18, was born female and is now male). They also write about their romantic relationship and their eventual breakup.

Katie and Arin also discuss their advocacy work for the transgender community, which is what Arin says drove him to go public with his story. “I survived transitioning because I had people to look up to also, like guys on YouTube,” he says. “And it’s totally worth it, because sometime every now and then, I will get a message about me inspiring someone, or quote unquote ‘saving his life,’ or making him have a little bit better day, or a better transition.”

How did they decide how much they could share about each other’s stories? “We had some boundaries at first,” Katie recalls. “But then after that, we threw our hands up and said, ‘You know, let’s just make this as honest as possible, and say what we need to say.”

There are some fairly personal stories in the books, including descriptions of sex with each other – something that Arin says they were always asked about in media interviews – and their surgeries. They provide details of their breakup, which Arin points out is an unusual thing to have to worry about becoming news. “You just broke up with that person, and in [most] teenage relationships you don’t have to worry about, ‘What’s this person going to write about me in their book?’ ” he says. “But this time you do.”

There were other complications for the young authors, too, such as how to balance the demands of being full-time students with writing an entire book. This was especially complicated because of a shortened publishing cycle. Trimmer says he wanted the books to come out quickly to capitalize on the couple’s public recognition – they appeared together in outlets including the Huffington Post and 20/20 last summer – as well as what he calls “a cultural moment happening,” as several other transgender stories made headlines. But this left Katie, then a sophomore at the University of Tulsa, and Arin, a high school senior, with only months to write their stories.

Trimmer brought in two veteran memoirists familiar with transgender issues, Ariel Schrag and Joshua Lyon, and paired them with Katie and Arin respectively. Even so, Trimmer says, books being written in near real-time demanded a detailed schedule, as well as some flexibility. For example, Arin’s story was supposed to end with his high school graduation, but they decided to take a new direction when he was honored with a youth leadership award by Tulsa’s Dennis R. Neill Equality Center – on the second anniversary of the day he began taking testosterone. “We were like, ‘Oh gosh, we’re doing that! Screw high school graduation! This is bigger,’” says Trimmer.

Now that the memoirs are about to be published, Katie says what she really wants is to help educate people, and make trans kids feel like there is someone in the world who shares their feelings and experiences – something she could never find in books growing up, even as an avid reader. She says she knows the book will receive some criticism, and some degrading comments, and she is ready for the reality. “My whole life I’ve had both people slandering me, and people on my side, rooting for me,” she says. “I understand that’s just how life is.”

Rethinking Normal: A Memoir in Transition by Katie Rain Hill. S&S, $17.99 Sept. ISBN 978-1-4814-1823-8

Some Assembly Required: The Not-So-Secret Life of a Transgender Teen by Arin Andrews. S&S, $17.99 Sept. ISBN 978-1-4814-1675-7