He wanted to design an attractive interface to transmit information in a simple way, for example, an icon to display weather forecasts rather than write ยซ cloudy ยป.
Kurita therefore drew a set of images of 12 pixels per 12 pixels that could be selected from a grid similar to a keyboard in the interface and then sent to mobile phones as their own characters. Kurita's 176 emoticons are privileged symbols on faces, as the goal 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 (fixed line, mobile phone, television).

The emojis and smileys quickly became popular in Japan, while rival mobile companies copied the idea of DOCOMO (NTT DoCoMo). Since mobile computing continued to explode in the mid-2000s, companies outside Japan, such as Apple and Android, had the opportunity to integrate Emoji and smiley on the keyboard of their platforms.
In 2007, a team of software developers at Google decided to lead the load, requesting that emoticons be recognized by the Unicode Consortium. It is a private organization that coordinates the development of the Unicode standard to maintain text standards on several computers. Unicode finally decided to index the emojis. It was the beginning of the legitimization of emojis as a form of communication. In other words, Emojis and smiley had become too popular to be ignored.
The blessing of the Unicode Consortium was not only a means of maintaining standards for the existing lexicon, but a standard that will guide the evolution of the emojis. In fact, every year new emoji are proposed and some are selected to be part of the emoji lexicon.
If you want to know more about emoji, I invite you to read The WIRED Guide to Emoji.