What is the 25th rule of shinobi?

Excuse me, could you please clarify what you mean by "the 25th rule of shinobi"? Is this a reference to a specific fictional universe or a set of guidelines related to cryptography or finance? If it's the latter, I'm not familiar with such a rule in the context of either field. However, if you're referring to a cultural or fictional concept, perhaps you could provide some more context or background information so I can better understand and provide an appropriate answer.