I’ll be upfront I have not bought this product and love cool shirtz but most of their products do Japanese well. This is not one of those products. It absolutely does not say “very cool” in japanese. I’m Japanese and cannot for the life of me understand what they tried to write. It looks like maybe 大レてクール? which is gibberish followed by “cool”. Maybe it’s 大してクール? which is a phrase at least but makes no cohesive grammatical sense and also means something close to “not very cool” (again the grammars weird so it just kinda means that lol)
I consulted my Japanese relatives to see if I was missing something on what was written but we all agreed we have no idea what it means to say. I love cool shirtz, I can confirm all other products I’ve seen from them use Japanese correctly, I have no idea why this one is the exception. Just figured I’d write this out in case the Japanese being correct was a big deal to anyone buying.