Professor was so impressed with Eimi Haga’s creativity, he didn’t reveal whole text

This article is more than 11 months old

This article is more than 11 months old

A Japanese student aced an assignment on ninja culture by making her own invisible ink from soya beans in a stealthy move that impressed her professor.

Eimi Haga, a member of Mie University’s ninja club, submitted an essay about the assassins with a message attached instructing the professor to heat it before reading.

“I knew that I needed to take it home and put it above a stove,” said Yuji Yamada, who teaches Japanese history, including ninja culture. “She replicated what is written in records of ninja art. She strived to prove what was written actually works and went through a trial-and-error process. I was impressed.”

When the characters of Haga’s essay revealed themselves in the heat, Yamada – who had promised his students extra marks for creativity – decided to award her an A.

Haga, 19, made the ink by soaking soya beans overnight and then squeezing them into a paste. She said she had tested three different kinds of paper for the optimum effect.

“If the paper is too thin, it burns when heated. If it’s too thick, it doesn’t absorb the ink very well,” she said. “I usually use pens and PC to write things. It’s been a while since I took a brush to write with an invisible ink.”

Yamada said reports filed as scrolls or folded into throwing stars were the most creative he had seen from students until now. “We discussed the use of invisible ink but I was amazed that someone actually used it,” he said, adding that he didn’t read the entire paper because he wanted to keep some of Haga’s work invisible.

“By learning about ninja … we can apply their knowledge and ways to modern society,” Yamada said.

Ninjas were agents revered for their ability to combine stealth and violence in the service of their samurai masters during the “warring states” period in Japan from the mid-15th century.