Abdullah Allywa allegedly approached the teen at Lidcombe Railway Station one morning in February 2025 and offered to buy her food.
The pair went to a nearby car park, where he allegedly sexually assaulted her while armed with a knife.
The 15-year-old fled the scene and Allywa, 22 years her senior, was arrested the next day at his home in Newtown, in Sydney's inner west.
After spending 10 months behind bars on remand, he appeared before the NSW Supreme Court on Monday to ask to be released on bail.
In an impassioned plea, Allywa, now 38, told the court he would place his hand on the Bible and swear not to disobey the law.
"I promise Your Honour I will not do anything wrong in my life," he said on the videolink from custody.
Allywa lives with an intellectual disability and mental health illnesses including schizophrenia, which make his time behind bars more onerous, his lawyer told the court.
DNA had not tied Allywa to the alleged offences while the knife had not been forensically analysed, despite a looming trial, the court was told.
"That (knife) could just be an object that was found there," Allywa's lawyer said.
But the crown prosecutor maintained the absence of DNA was consistent with the allegation that the 15-year-old had been assaulted through her clothing.
He opposed bail, citing the serious allegations and Allywa's previous convictions.
Arguments about his mental health were a "double-edged sword", the prosecutor said, because they demonstrated a need for supervision if released.
Justice Edward Muston acknowledged the 38-year-old would be able to better manage his mental health if released from custody.
But he denied bail, determining the risk to the community could not be mitigated by imposing house arrest conditions on Allywa, who lives alone.
The 38-year-old will remain behind bars until he faces his NSW District Court trial in July.
He has pleaded not guilty to aggravated sexual assault of a victim under 16 and two counts of intentionally sexually touching a child between 10 and 16 years old.
Credibility will be a major issue during the trial, the court was told.
Allywa contends the complainant told him she was 19 years old.
1800 RESPECT (1800 737 732)
National Sexual Abuse and Redress Support Service 1800 211 028
Lifeline 13 11 14
Kids Helpline 1800 55 1800 (for people aged 5 to 25)
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