is it a yakuza fish?! よこせ gives the feeling of like "hand it over!" or "fork it over!" like... fork over the cash! but books? it seems like that mackerel has an intense desire to read...

You may have wanted to use the QA section. Anyway, 新刊（しんかん）: new book(s), newly-published book(s), new publication(s)　よこせ: Give me (plus quite rude expression). 新刊をよこせ: Give me (the/a) newly-published book(s). Weird message to me as a T-shirt print.