[This is not exactly a translation but more a re-imagining of 『三角と四角』 ("The Triangle and the Square") by IWAYA Sazanami (巌谷小波). As you might guess from those links, I'm working from the Aozora text.]

The Foolish Triangle

There was once a triangular ruler, the kind you might use while learning geometry, who was very proud of the fact that he had three sharp corners.

"The world's full of stationery, but none of it has more corners than me," he would say to himself smugly. "When it comes to angles, I'm number one!"

But one day, a pencil that lived in the same desk came up to him and said, "Yo, triangle! Triangle! I always thought that no-one had more corners than you, since you brag about them so much, but did you see the drafting board that arrived just before? It's got you beat, dude."

"I beg your pardon?" said the triangle, frowning. "More corners than me? Stop talking such nonsense. It's a wide world, but nobody in it is pointier than I."

"Whatever, dude," said the pencil. "I know what I saw."

"Perhaps there is something wrong with your eyes."

"Hey, if you don't believe me, go look for yourself."

"Very well, I shall. And I shall know if you're lying."

"Fine with me, because I'm not."

And so they went to look, and the triangle had to admit that the drafting board had four corners -- one more than him. What's more, all of the rest of the stationery, that had always looked up to the triangle before, was now gathered around the drafting board admiring its corners instead.

"Boo-yah!" said the pencil. "You see, dude? I told you it was true."

"All right, all right, you win" muttered the triangle. Because really, what else could he do? Still, he was a bad loser. Miserable little board, he thought, barging in where you weren't invited, with your fancy corners. You'll pay for embarrassing me like this. And before long the perfect plan for revenge occured to him.

So, on the way home, he stopped at the scissors' place.

"Scissors, old friend," said the triangle "Can I borrow you tonight?"

"I guess so," replied the scissors. "But what do you wanna cut?"

"Something quite hard, as it happens," the triangle said. "How's your edge?"

"I'll cut most anything, but if you think it'll be a problem I could sharpen up a little before we leave."

"Perfect! Let me sharpen you just a smidge," said the triangle. "This might sting at first, but it can't be helped and it won't take long."

And so the triangle sharpened the scissors until they seemed sharp enough, then went home and waited impatiently for the sun to set.

Eventually, it did, and night fell. Once the whole desk seemed to be asleep, the triangle crept out of bed. Heart pounding and scissors under his arm, he tiptoed stealthily over to the drafting board.

It was dead to the world and snoring like there was no tomorrow. Perfect! thought the triangle. Now, my four-cornered friend, I shall cut off every last one of your points, and as of tomorrow I shall once more be the King of Corners.

Snip! went the scissors, and off came one of the drafting board's corners. The board didn't seem to notice, though, so the triangle snipped off another. The drafting board still didn't wake up. "Well, aren't we a sound little sleeper," snickered the triangle, and with a final snip! snip! he cut off the board's last two corners.

"Thanks ever so, scissors," the triangle said, and he hurried back to his house and fell fast asleep.

The next morning, he left the house looking as innocent as he could. The desk was abuzz. Everyone who saw him said, "Have you seen the drafting board? It's totally awesome!"

What the devil--? thought the triangle. Wondering what had happened, he went over to see for himself, and found the drafting board strutting around proudly -- for not only was he not cornerless, he now had eight!

Of course, we all know that cutting off four corners will only make twice as many, but the triangle was no geometer. "That oblong magician has turned octagonal in a single night!" he said to himself, shocked. "If this keeps up, by tomorrow he'll have ten -- maybe even twenty corners! Bah! I may as well give up!"

And that is just what the foolish triangle finally did.