Judge Geoff Rea said the victim chose to "check out" to protect herself. "She did not respond as she thought if she fought, screamed or resisted she would be subjected to violence."
A police investigation was launched but it wasn't until years later that a positive DNA test came up with a match.
Defence counsel Rennie Gould made a prolonged submission to argue a prison term would be "meaningless". She pushed instead for a "punitive" sentence of home detention for her client, who was aged 20 at the time of offending yet had "the mental age of someone much younger".
She said despite his earlier cognitive issues he had since led a model life with the help of a supportive Christian family, had obtained his driver's licence and held down two jobs.
She claimed prison would be fruitless as it precluded any real hope of rehabilitation. "If he goes to jail she's [victim] not helped, he's not helped."
Asiata had been assessed as a "nil to low" risk of reoffending and his family had offered $5200 emotional harm reparation.
Prosecutor for the Crown, Clayton Walker, said there were many intellectually impaired people in the country "who did not offend in this way".
"So you simply cannot say that he's intellectually impaired and therefore should not face the sanction that is otherwise imposed," Walker said.
"A large number of intellectually impaired people in this country would be offended by that suggestion."
He argued for a prison term, citing the protection of the community and the victim's wish for accountability.
Judge Rea said a "harrowing" victim impact statement had been provided to the court.
"The statement highlights the terrible effects these crimes have on victims."
He said he took into account Asiata's cognitive difficulties, yet said the court didn't find any "causal nexus" between his impairment and his crime, and that his intellectual challenges didn't amount to a "lesser moral fault".
In addition to the prison sentence he ordered immediate payment of $5200 to be paid to the victim.
SEXUAL HARM - DO YOU NEED HELP?
• Lifeline: 0800 543 354 (available 24/7)
• Youthline: 0800 376 633
• Whatsup: 0800 942 8787 (1pm to 11pm)