A Bristol University student and her partner will take part in every Olympic sport over the 17 days of the Tokyo Games to raise money for charity.
Charlotte Nichols, who is studying to become a doctor, and Stuart Bates, a window cleaner in Oxford, believe they are the first to take on the feat - that will see them run, throw and jump their way through almost 100 sports.
The challenge will include a 50km speed walk, 10km swim, 240km road cycle and a marathon.
They are doing it in memory of Mr Bates' brother, Spencer Bates, who died in 2011 from motor neurone disease.
The father of two, also known as Spenny, was 49 when he died and inspired the couple to do something for charity during the Olympic games.
They aim to raise £10,000 for the Motor Neurone Association during their challenge, which they have aptly called the 'Spennylympics'. They have already raised more than £8,000 towards their goal.
"We're terrified and excited at the same time," said Miss Nichols, 21.
"It's been a real journey already - we've had to learn loads of new sports and we've met some amazing people along the way.
"The training has been tough, particularly fitting it around studying medicine. But there have been some incredible moments too, like sailing in Weymouth as the sun was setting.
"It has been a chance for us both to think about Spenny a lot too. When you're feeling achy and tired and you don't want to go out and train, having him in your mind really helps."
The couples' adventure will start on 23 July and they will take on 96 sports in 17 days.
Much of their challenge will take place across the West Country, including Bath for track and field, and The Wave near Bristol for surfing.
They will also go sailing and windsurfing in Weymouth - the home town of Mr Bates' brother - and play a football match with his friends and family.
On the final day of their challenge, they will take on the marathon.
Mr Bates said his brother, who died leaving wife Nicky and two sons Samuel andIsaac, was "a truly one-off character".
"There is not a day goes by that his presence isn't missed and we will continue to do everything that we can to raise money so that a cure can be found for this brutal and 100% fatal disease," he added.
Since his death, the family has raised more than £100,000 for the Motor Neurone Disease Association. The couple has recruited more than 55 former and current Olympians to beambassadors for their challenge, including rower Ollie Cook, pole vaulter HollyBradshaw and runner Sally Gunnell.
Others have offered lessons in sports from canoeing to rhythmic gymnastics, while the University of Bristol has given the pair free run of its sporting facilities.
Miss Nichols said she would find the 10-metre dive "daunting" but would get through it.
Mr Bates added: "There are so many events where there is a real danger of injury, so we will need a huge slice of luck along the way.
"Staying on the horse whilst showjumping is something giving me sleepless nights."<
The couple's JustGiving page can be found here.