This aligns with what I was taught in my U.S. Intellectual property class a few years ago
Japan's very lucrative doujinshi (read: fan novels) and fan art scenes exist purely because most of the creators and publishers turn a blind eye to them (it's free marketing and good will from fans of their works). They only start caring if the fan works are being sold for profit or harming the original IPs.
Comiket exists thanks to everyone knowing and respecting where the invisible lines in the sand are drawn.
Permission is absolutely required in Japan, legally speaking. In practice, the requirement for permission is ignored under gentlemen's agreements.