This is actually a valid question that was recently brought up. For any kid of the 80s or 90s, Rainbow Brite was a fundamental part of watching cartoons or buying greeting cards.
In 1983, Hallmark Cards introduced this colorful little girl to aide in sales. Her artists were Garry Glissmeyer and Lanny Julian. The gimmick worked - by 1984, she had her own cartoon series as well as a licensing agreement for merchandise by Mattel.
This catapult to fame gave her some additional characters that could also be considered 'kawaii':
Twink, her personal sprite/guide and best friend.
And the Color Kids - who rely on her guidance and leadership to protect their magical town from the evil Murky and Lurky, who wanted nothing more than to banish color, fun & beauty.
So as we know, this series was American-made. However, it reached all the way to Japan and instantly became popular, likely due to 2 factors:
The evident 'Chibi' (short/round) style of the characters, and
The 'magical girl' element of the show, which is popular in anime.
In fact, the Japanese even gave her their own name:
Magical Girl Rainbow Brite (魔法少女レインボーブライトin Kanji, , pronounced like: Mahō Shōjo Reinbō Buraito?),
Even in our modern age, she still makes appearances on cartoons, kid's books, and even collectable items. However, she's been elongated and lost the adorable 'chibi' quality she once had. A lot of fans prefer the original 80s version.
Join the debate and let me know what you think: Could Rainbow Brite be considered 'Kawaii'?
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