The latter wanted to design an attractive interface to convey information in a simple way, for example, an icon to display weather forecasts rather than writing "cloudy".
Kurita therefore drew a set of 12 by 12 pixel images that could be selected from a keyboard like grid in the interface and then sent to mobile phones as their own characters. Kurita's 176 emoticons, are privileged symbols on faces, as the objective was to find new ways to express information. There were icons to show the weather (sun, clouds, umbrella, snowman), traffic (car, tram, plane, boat), technology (landline, mobile phone, television).
Emoji and smiley faces quickly became popular in Japan, as rival mobile companies copied DOCOMO's (NTT DoCoMo) idea. As mobile computing continued to explode in the mid-2000s, companies outside of Japan, such as Apple and Android, had the opportunity to integrate emoji and smiley faces into the keyboard of their platforms.
In 2007, a team of software developers at Google decided to lead the charge, requesting that emoticons be recognized by the Unicode Consortium, a private organization that coordinates the development of the Unicode standard for maintaining text standards across multiple computers. Unicode finally decided to index emoji. This was the beginning of the legitimization of emoji as a form of communication. In other words, emoji and smiley had become too popular to be ignored.
The blessing of the Unicode Consortium was not only a way to maintain standards for the existing lexicon, but a standard that will guide the evolution of emojis. Indeed, every year new emojis are proposed and some are selected to be part of the emojis lexicon.
If you want to know more about emoji, I suggest you read The WIRED Guide to Emoji.