MARION — When Derek DeCosta first arrived in Hyannis, he was scared and alone. He did not speak English. He did not know where he was or why his parents had abandoned him. He didn’t even know yet that his name had been changed from Yoon Sang Kyun.

DeCosta recounts in his newly published book, “The Moonlight King,” that he was just six years old when his parents put him up for adoption in Korea. They preferred to send him to America along with his older sister, rather than facing the shame of their divorce. But that was only the beginning of the challenges he would face.

DeCosta and his sister were not taken in by a happy family that would give them a better life, as their parents undoubtedly hoped. In reality, their new family was made up of one monstrous woman, her violent and abusive son, and a herd of cats that held a higher social status within the house than him or his sister.

For the eight years he lived in that house in Hyannis, he was regularly abused physically, mentally and sexually, until one day he escaped.

Most people who know DeCosta, as he lives now in Marion, probably would never have guessed that his life began with such unrelenting torment. When you look at him today, you will see only a confident man with good posture, a warm smile and a knack for conversation.

That is because DeCosta doesn’t carry those injustices with him anymore — he decided to let them go a long time ago, along with his dreams of revenge. He has learned to accept what happened to him and has realized that without it, he wouldn’t be who he is today. But he has not forgotten about it either.

Eight years ago, DeCosta, now a fitness trainer, was asked to write a blurb for a workout video he filmed that was going to be redistributed in Korea. However, the marketers thought that Koreans might be confused by his distinctly un-Korean name and wanted him to give a short explanation of how he came to be known as Derek DeCosta.

The short blurb, however, turned into an eight-hour marathon writing session as DeCosta began to put his memories down in print for the first time. After two weeks, he had written almost an entire book, though the editing process took considerably longer.

He finally self published the book earlier this year under the title, “The Moonlight King.” The name references both his affinity with the moon — which always made him feel protected and closer to his mother as a child — and his innate feeling that he was meant for something greater, which sustained him during low points in his life. 

“As I wrote this book, what I realized was that the freedom I was searching for wasn’t a physical one like I thought it was when I was younger,” he said. “Physically I left the house, physically I got my body stronger as I trained to defend myself, but the real attack wasn’t physical anymore. It was all emotional.”

DeCosta said it was not until he realized how much baggage he was still carrying that he could finally put it down. Once he did, he wanted to help others do the same.

“One of my objectives with this book is for people to read it and say, ‘you know what, I need to let go of these demons that are not serving me anymore, I need to forgive the people who hurt me and I need to live a life that is filled with passion and love,’” he said. “I really believe the point of life is to give and receive love, but you can’t do that when your heart is filled with fear, anger, frustration or resentment. So you have to let those things go to create the space for love to exist.”

DeCosta is a teacher now. And as any good teacher does, he uses the lessons of his life to help his students better understand their own.

His fitness and self-defense classes are held at his private studio in Marion. The sessions involve a mix of stretching, cardio, strength training, meditation and wellness coaching that he tailors to fit each student’s goals. Through his work, he says he strives to help his students develop themselves not only physically but mentally, emotionally and spiritually.

“I model myself after the samurai code of ‘constant improvement,’ which is a word that I use in my book, ‘kaizen,’” he said. “Kaizen is a Japanese word that means 1% improvement in every facet of your life, every single day. And the idea is that if you improve yourself in every way by 1%, even when no one’s looking, you are by default 365% better by the end of the year.”

DeCosta’s book, “The Moonlight King,” is available on Amazon in paperback or kindle format. To contact him to schedule a free consultation, call (508) 930-1861. To learn more, visit his website at kikfit.com or themoonlightking.com.