The design for Pikachu, one of the main characters in the popular game franchise Pocket Monsters, better known as Pokemon, was based on a squirrel — not a mouse — developers of the game have told The Yomiuri Shimbun.

This is the first time the designers have revealed the story behind Pikachu’s origin. The game debuted in 1996.

The Pokemon Co., the Tokyo- based brand management company for the Pokemon franchise, will add this information to its website as early as late May.

Pikachu has been a fixture of the franchise since the first Pokemon game debuted in February 1996 for Nintendo Co.’s Game Boy handheld game console.

Ken Sugimori, 52, was an executive at game developer Game Freak Inc., and Atsuko Nishida was working as an illustrator at the company when Pokemon was released. Nishida was tasked with designing a “cute monster” character that was an “electric type” that used electric attacks and had two additional forms of evolution.

Nishida said she initially created a character that resembled a “vertically long daifuku rice confection with ears.”

After being told it needed to be cuter, she created a new design based on a squirrel, an animal she wanted to own as a pet at the time.

Nishida eventually created the prototype design for what would become Pikachu using large pixels on a computer screen, while Sugimori drew the illustrated version. The initial daifuku-like character, which Nishida also drew using large pixels, was erased and no longer exists.

The character’s name combines the words “pika,” an onomatopoeic term for flashing light, and “chu,” which the creators thought had a cute sound. Although the character was not modeled after a mouse, Game Freak President Satoshi Tajiri called it a mouse character.

Among the more than 800 “pocket monsters” available today, Pikachu is still classified as a mouse character.

“I hope people will feel closer to Pikachu by understanding the story behind its creation,” Nishida said.