A man died in a "terrible, awful, tragic accident" after being left with a gas mask around his face and tied at his hands, feet and neck by his sexual partner, a court heard.
Dohoon Kim, 36, allegedly died from a combination of the restriction of his airways and the effect of drugs both he and friend Kevin Adams, 52, had taken.
The pair had taken mephedrone, known as M-Cat, and GHB, before engaging in "extreme" sexual activity at Adams' home in Swindon, Wiltshire, on June 12 2015.
Adams denies Mr Kim's manslaughter by failing to ensure his safety and well-being, which prosecutors say he was responsible for during and after sex.
He fell asleep on his bed without removing the gas mask or restraints from Mr Kim - steps that could have saved Mr Kim's life, Bristol Crown Court heard.
Emergency services attended Adams' terraced home after he called 999, reporting that he had found Mr Kim unresponsive and not breathing.
Paramedics attended at 2.12am and found Mr Kim, from Slough, Berkshire in the UK had been dead for some time and could not be resuscitated.
Pavlos Panayi QC, representing Adams, said his client had not chosen to fall asleep but had "passed out" due to drugs and physical exhaustion.
"Kim died two years and three days ago as a result of what everyone in this case will agree is a terrible, awful, tragic accident," he told the jury.
"Kevin and Kim met to have sex. They had met before and taken these drugs and had the same kind of fun in the past.
"No one was hurt before and no one wanted or expected that anyone would get hurt that night. They had met 12 times before. This was the awful, unlucky 13th time."
Mr Kim was born in South Korea and moved to the UK in 2001, meeting his partner Mark Ciccone a short time later. The couple began living together in 2012.
Jurors heard Mr Kim was a "submissive" who regularly met "dominant" men - including Adams - for sex, with the permission of Mr Ciccone.
He travelled from work in Slough to Adams' home by train and taxi on June 12, arriving there at about 8pm.
Text messages between the pair, who had met about two years previously on a dating website, refer to being "chemmed-up" - having sex while taking drugs.
Mr Panayi, in his opening statement to the jury, said Adams was "very unwell" and grey when paramedics arrived to treat Mr Kim.
"Could Kevin have stayed awake if he had tried and wanted to or did he pass out - did they both just pass out?" he said.
"It is his case that he passed out. You might not find it surprising given the amount of drugs he had ingested and the strenuous sexual activity for hours and hours."
He said the restraints around Mr Kim's wrists were velcro straps, designed for "easy and quick release", and secured with a carabiner.
"If both men knew that he could take it off if he wanted to, is it accurate to make Kevin Adams responsible?" he added.
A post-mortem examination found Mr Kim had low levels of GHB in his body and an "excessive" level of M-Cat, prosecutor Adam Feest told the jury.
Mr Feest said Adams failed to remove the gas mask or restraints or check the condition of Mr Kim, who was left lying on the floor, before he went to sleep.
"Many things that could have been done, that could have been potentially life-saving, but not done in this case," Mr Feest added.
Police analysed text messages between Adams and other sexual partners following Mr Kim's death.
"It is clear that he has a liking for extreme sexual activity, particularly bondage, corporal punishment and breath control," Mr Feest said.
"The practices which he indulged in are inherently risky, dangerous and unpredictable."
Jurors have been repeatedly told that the sexual activity between Mr Kim and Adams was consensual at all times.
The trial continues.