The professor, Yuji Yamada, told the BBC he was “surprised” when he saw the essay.
“I had seen such reports written in code, but never seen one done in aburidashi,” he said.
“To tell the truth, I had a little doubt that the words would come out clearly. But when I actually heated the paper over the gas stove in my house, the words appeared very clearly and I thought ‘Well done!’
“I didn’t hesitate to give the report full marks – even though I didn’t read it to the very end because I thought I should leave some part of the paper unheated, in case the media would somehow find this and take a picture.”
As for the essay itself, Ms Haga said it had more style than substance.
“I was confident that the professor would at least recognise my efforts to make a creative essay,” she said.
“So I wasn’t really worried about getting a bad score for my essay – though the content itself was nothing special.”
Additional reporting by the BBC’s Hideharu Tamura in Tokyo