This tee was made to celebrate the short animation "Chao in Space", that Sega did. As you'll know "Chao in Space" is the 'movie' that you always saw as a movie poster decoration around various levels/various games when they wanted a billboard or other 'advertising space' as part of the level.
Well, Sega decided it was going to actually 'make' it, and you can find/watch it on their Youtube. However, it turns out that it is all a dream by a neutral chao. This tee, in the Sega Shop at the end of 2019, is about 24 dollars and was produced to help hype the short.
It's a plain gray tee with black/line art only of Sonic sitting under a palm tree with coconuts, and the neutral chao that dreams up the story is sleeping next to him. Sitting/relaxing Sonic isn't all that common, so it's an ok and different shirt, even if it's not all that dynamic.