In order for Shinobi to learn some jutsu such as custom jutsu, special jutsu, or even canon jutsu that are above your rank there is a way to learn them instead of them being impossible to attain.
That method is simply being trained by a master, sensei, scroll given to you, etc.
However not to make it too easy you will of course have to make a thread learning said jutsu and each rank requires a certain word count.
C-Rank: 500 Words
B-Rank: 1000 Words
A-Rank: 2000 Words
S-Rank: 4000 Words
These do not account for Special Jutsu however. Seeing as how none have been purchased, there will be a different topic for those jutsu.