A young man was stalked through central Dunedin for a kilometre before he was attacked and sexually violated in an alleyway and the grounds of a church.

Alex Aleti Seu will spend at least the next four years behind bars after being jailed for a violent sexual attack on a young man and the indecent assaults of two former flatmates.

The 30-year-old, who identifies as transgender, was jailed for six years and nine months with a minimum non-parole period of four years during an appearance in the Dunedin District Court yesterday.

Seu had been at a screening of The Rocky Horror Picture Show at the Regent Theatre on the night of June 25, while the victim had watched the All Blacks' test game against Wales.

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The pair were in the Octagon in the early hours of the following morning, when the victim left to walk to a friend's flat in North Dunedin.

Seu started following the victim down George St, according to a summary of facts.

"As they approached Albany St, the defendant quickened his pace and caught up with the complainant on the corner of Albany and George St," it said.

"The complainant turned into Albany St and as he did the defendant grabbed on to his arm and dragged him into a dark alleyway."

Seu threw the heavily intoxicated victim into a brick wall, stunning him in the process. Sexual acts were then performed on him. The young man managed to break free and momentarily escape.

Seu pursued the victim down Great King St and forced him into the grounds of a church. There the attack continued.

The victim suffered injuries as a result of the attack as well as suffering from "severe psychological" impacts, Judge Kevin Phillips said.

"This has had a major impact on his life," Judge Phillips told Seu during the sentencing.

The indecent assaults against Seu's former flatmates took place on August 10 and August 18 last year after Seu's arrest for the sexual attack.

The court heard a pre-sentence report assessed Seu as potentially being a high-risk of reoffending.

However, Crown prosecutor Craig Power said the word "potentially" understated Seu's risk of reoffending, saying Seu was actually "high risk".

Defence lawyer Sarah Saunderson-Warner said Seu's offending was opportunistic.

But Phillips dismissed that notion, saying it featured a "high-degree of premeditation, determination and violence".

It was revealed in court yesterday that Seu "considered the encounter consensual" until reading the victim impact statement.

Phillips dismissed the suggestion the interaction could be construed as consensual.

"It was an attack by you on a man that you selected as he was highly intoxicated," he said.

Seu was jailed for six years and nine months on the most serious sexual violation charge, four years' jail on the secondary sexual violation charge against the same victim and one year for each of the three counts of indecent assault on the flatmates. All sentences will be served concurrently.

Seu shook her head, covered her mouth with her hand and had a look of disbelief on her face as Phillips read some of the details of the offending.

Seu pleaded guilty to the offences in January. Seu will not be eligible for parole until at least 2020.