for stuff you bought on DLsite, can other people play it if it doesnt have DRM?

It says on the product page if the game is protected or not, if its not others can play it too.
You can also share protected games since maybe someone can crack them, just let people know that they are protected and use the search function here on the forum with japanese and english title to make sure game isnt shared yet.


https://cs.dlsite.com/hc/en-us/articles/1500003137842-About-soft-denchi
Soft-denchi (have to install extra software for viewing and then typing in serial number for the game)

https://cs.dlsite.com/hc/en-us/articles/1500003131062-What-is-PlayDRM-
PlayDRM (have to type in serial number after double clicking game exe file)



https://cs.dlsite.com/hc/en-us/articles/1500003008782
Mostly for comics if you wanna view it offline you have to install special software.

These are the ones I know, there might be a few more, you can read all about it here:

https://cs.dlsite.com/hc/en-us/categories/1500000145381-Product-Troubleshooting

(regarding your question "I think they have a notorious one that requires you to have a Japanese IP address to activate?" Your OS has to be set to japanese for non unicode programs for a lot of games to work or you can try to run game with locale emulator and japanese language pack should be installed for windows. Japanese IP is not necessary as far as I know, the only time where you would need one would be if the online store where you would want to purchase a game from is region blocking you from accessing it like dmm and a few others do for example. And some japanese online only browser & mmo games might need japanese IP too so you can play them)