trap15 wrote:As said many times before, they are obligated to send desist letters otherwise they lose enforcement of the trademark (and copyright? forget).
Trademark needs pretty much constant protection, since trademark length is indefinite, and everything I'm reading up about it makes me feel like any famous trademark owner should be in a constant state of panic since there are a lot of things that could dilute the mark and cause it to no longer be valid. On the other hand, since Xerox, Hoover, and iPod are still trademarks [somehow], I'm pretty sure it'd take a bit more than I'm thinking for a trademark to be lost.
There's a gray area regarding parody and particularly around fan-works, which typically flutter in/out of being in the realm of trademark parody protection.
On the other hand, copyright doesn't, and an author is pretty free to act [or not act] as they will with their property without losing their rights over it. Ostensibly, copyright length is finite [

] and has a fixed minimum length. Just because someone else uses your work and you do nothing doesn't stop it from being under copyright protection if you do decide to do something about it later on [although it may affect how much you can receive when suing].
mamboFoxtrot wrote:Aren't Touhou's characters/music/etc considered public domain, though?
Nope! ZUN set up some specific guidelines of his own for use in fan works, and he either turns a blind eye/doesn't know about a fair couple of things.
on a vaguely related note, the Vocaloids [Miku, Len, Rin, Luka, KAITO, MEIKO] are CC BY-NC licensed, so you can pretty much do whatever with them other than sell shit using them