Psst. Have you heard how Hollywood studios are in cahoots with a company that secretly owns 4chan? And they’re helping prop up a website that surreptitiously traffics in sexually explicit figurines of underage female characters? If not, it may only be a matter of time before this wild tale travels far thanks to an eye-opening court document filed in L.A. earlier in September. The filing comes amid, of all things, a dispute involving Netflix’s Stranger Things.

Japan-based Good Smile is the main player here. The company, which grew out of the anime world, manufactures pop culture toys and has ...