I mostly bought the souvenir towel because it was (to my eyes) such a strange item to offer as merch. And yet, souvenir towels are definitely a thing for lots of Japanese bands. My understanding is that there are situations in Japan where you're expected to bring your own hand towel for hygiene purposes, though I didn't know this at the time and didn't encounter any public restrooms that didn't provide paper towels or somesuch. I also didn't venture much outside of Tokyo, so that might have something to do with it.
Anyhow, don't forget to check out my playlist for this comic, which includes several Mejibray songs, as well as all the bands featured on t-shirts in the background (for this page, that would be The GazettE, OZ, X, and Exist Trace): https://www.youtube.com/playlist?list=PLYvv_X5qp4EyrOtVkosEwxlxh1e4cVnhZ
p.s. - X, known here in the U.S. as X Japan for legal reasons, is one of the most famous of all visual kei bands, and is still so well-regarded I saw X merch at the 7-11 (or possibly Lawsons of Family Mart, I don't remember which). Sort of the equivalent of finding Metallica posters at your local convenience store.