He allegedly wrote "I want to sleep with you" and "I'm feeling horny".
He was also accused of asking the student: "send me a photo of you masturbating".
The student met Mr Nagashima when he accompanied students to the Japanese sister school.
On September 12 2015, the student was surprised to receive a message on Facebook from the teacher. She had not had much interaction with him during his visit.
In the first message Mr Nagashima asked her about flood damage following a typhoon.
He then began sending inappropriate messages which the documents said embarrassed and scared her.
The messages were only sent on September 12 2015 and there was no communication that followed.
"The student did not initiate the Facebook conversation with Mr Nagashima and did not give him any reason to think that she would sleep with him, have sex with him or send him photographs of herself masturbating," the documents said.
On September 14 2015, the student told a teacher about the messages and gave him a copy of screenshots she had taken of the messages.
She reported the messages because she said she was afraid of what he may have done or said when he was due to visit her school again two months later.
She deleted the messages because she did not want "to see the terrible content anymore".
The documents said the student deleted her Facebook account because she feared Mr Nagashima would contact her again. He resigned from Beaconhills College after the school was informed.
The messages
The documents revealed a more detailed transcript of the conversation between the student and Mr Nagashima.
He said: "I hear that the floods were bad. Was everything OK where you are?".
She responded: "Long time no see! Yes! It was really bad, almost like a tsunami."
Mr Nagashima said: "Oh OK. That's good to know! By the way, I'll be there again in November this year."
The student wrote back and said she was looking forward to November and ended the message with a laughter emoji.
Mr Nagashima then said: "Now that you're a second-year student, you can't be a host anymore, right?"
She replied: "Yes I can! Apparently, it's allowed as long as you don't mind being busy before the trip."
He said: "Really? I thought it was only for first-years?"
She responded: "Last year two second-years hosted too".
The conversation then began to become inappropriate when he said: "Serious? Well then, host me as well."
She wrote back: "Teachers are out of the question [laughter emoji]."
He then said: "I want to sleep with you [student].
"I feel horny.
"Student?
"Send me a photo of you masturbating.
"Are you asleep?"
The teacher had initially claimed he was hacked. He had also claimed he had been drinking when he sent the messages but later denied saying it.
In his hearing, Mr Nagashima accepted full responsibility for the messages.
"I fully accept those wrongdoings, and messaging her regarding sleeping in her bed and talking about staying in her house, which is totally inappropriate, I apologise for these and the stress and discomfort I have caused to the student and everyone else involved," he said.
He also claimed some of the messages had been altered and some parts deleted, but did admit to saying he was horny and suggesting he wanted to sleep in her bed.
His teaching registration is suspended until February and he will visit a psychologist at least four times.
He is also ordered to write a report outlining why his behaviour was inappropriate and how he will stop it happening in the future.
