Here is a slightly older pair of underwear.
It's from the "Primark Essentials" line, and has appeared in a multi pack on Gear. Here, you can see one pair by itself, and how it holds up as well. This has been worn a lot, but, as you can see it remains mostly bright and unfaded, though the fabric has become very slightly pilly. The elastic waistband didn't quit or become ragged which is also nice.
The front has 3 different poses for classic Sonic (including neoclassic art) and a sort of 'fireworks lines' theme for the background. The back has neoclassic impatient/waiting Sonic with his name spelled out in Japanese...twice. The first is "Sonic the Hedgehog", and then "Sonic". (It doesn't make much sense but they had to fill up the other half of the fabric with letters I guess.)
The cloth tags inside are surviving well too from the wear, as is the logo on the front of the band. The over-all look is nice, colorful and actively designed. There's nothing at all generic about this underwear. It's nice to see the result of quality Sonic merchandise.