This is pretty simple and I expect you all as literate roleplayers to understand the meaning behind what this rule marks.
ALL Rinnegan users will die, period, for the sake of the storyline. It probably won't happen for a very long time but please don't let this put you off. The only one who will not die will be the holder in Tasogare, the leader, as it is his goal to recreate the power of the Rinnegan for himself.

This being said before any demons will be open for application all Rinnegan spots must be filled first. Treat the paths with respect and a realistic approach; even with the Rinnegan your genin is still a genin and unless otherwise ranked the abilities given by the path will be given a rank based on your characters level; Genin would be D, Jounin would be B/A etc. You can have both a demon host and one of the 6 Rinnegan users, that is fine, but please do not apply for demons until they are open.

All Tasogare members will eventually die off, as well. Do not apply for one if you are not happy with this. If it gets to the point in the story where we've killed off those who were happy to die and your character is still alive, we will be forced to tell you to die - which no one wants to have to do. Keep this in mind while creating mini plot arcs for your character; don't map out anything huge, since they will die eventually too.

Tasogare members each have a Rinnegan user to capture, you may have two characters to fill each of these roles respectively but you may not have them fight - ever. Your Tasogare member must pursue another holder in fairness. In other words, don't get yourself stuck in a situation where you're RolePlaying with yourself.

In summary; do not apply for a character role if you're not okay with your character dying for the sake of the plot, but please don't let this put you off. You can always make a new character afterward!

Thank you for reading!