Five of the counts are representative, alleging the abuse happened on multiple occasions between 2013 and 2015.
Crown prosecutor Craig Power said the defendant would spend significant periods of time with the girl and she would often spend the night with him.
"He was a man trusted implicitly and from the evidence you'll hear, the Crown says he used that trust to sexually abuse the complainant," Power told the jury.
The alleged offending came to light when the girl complained to her mother about feeling pain in her genitalia in August 2015.
She was interviewed by police twice and talked about the man initially touching her legs in the car as he drove.
"He says my skin is soft, that's why he likes touching me," she said.
"That's why I wear long pants."
The complainant also described "rough games" the man would play with her.
"He would always pull down my pants and touch my bum. I didn't really want to do [the games] because I didn't like him touching around there."
But defence counsel Anne Stevens said her client never molested the girl.
"The complainant is a child who has had a life full of insecurity and instability," she told the jury.
Stevens also asked jurors to pay attention to the circumstances surrounding the emergence of the allegations.
The girl only "created a story", Stevens said, after being repeatedly asked by her mother whether she had been abused.
The complainant had a different explanation in her evidence.
"Mum asked me twice. On the third time I started crying because I couldn't hold it in anymore," she said.
Despite the claims of prolonged abuse, the girl said she did not hate the man.
"I thought if I told anyone, he'd go to jail," she said.
"I didn't want him to go to jail or anything like that. He's really nice to us and it's just that I care about him a lot."
Power said one of the 20 witnesses, paediatrician Dr Jennifer Corban, would tell the court no abnormalities were discovered during genitalia examinations.
But Power said there were several explanations for that, which would be outlined to the jury.
The trial, before Judge John Macdonald and a jury of seven men and five women, is expected to run for a week.