'Ninja' student receives top marks for her blank essay paper

For most students, turning in a blank essay paper would be a guarantee of failing the class, but Eimi Haga from Japan is no ordinary student.

Haga, a student of ninja history at Mei University, received top marks for her work after her professor discovered she had written it all in invisible ink.

Haga used the ninja technique of "aburidashi", a time-intensive process which involves soaking and crushing soybeans to make the ink.

When her professor held the paper over a gas stove, her words were revealed.

"It is something I learned through a book when I was little," Haga told the BBC. "I just hoped that no one would come up with the same idea."

Eimi Haga, ninja student. Photo / BBC

Haga said she has been interested in ninjas since watching a TV cartoon as a child took a class in ninja history when she enrolled at university.

Haga was asked to write about a visit to the Ninja Museum of Igaryu and when her professor told the class he would give high marks for creativity she settled on the novel technique.

"I decided that I would make my essay stand out from others," she said.

"I gave a thought for a while, and hit upon the idea of aburidashi."

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.

The essay, showing heated and unheated sections. Photo / BBC

"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."